Pregnancy Blood Tests: The Complete Clinical Guide (2026)

1. Introduction
Blood testing is central to modern prenatal care, but there is no single “pregnancy blood test.” Different assays answer different questions: confirming pregnancy, evaluating an early pregnancy when symptoms or ultrasound findings are uncertain, screening for fetal chromosomal conditions, assessing maternal anemia and iron status, detecting infections, screening for gestational diabetes, and evaluating suspected pregnancy complications.
This guide summarizes current evidence and guidance available through September 2026, including recommendations from ACOG/SMFM, NICE, the American Society of Hematology (ASH), the American Diabetes Association (ADA), CDC guidance, and peer-reviewed research on cell-free DNA (cfDNA) and emerging cell-free RNA (cfRNA) biomarkers.
Because recommendations differ by country and clinical setting, tests described here should not be interpreted as universally mandatory. Timing, thresholds, follow-up, and treatment should be individualized.


2. The Foundation: Human Chorionic Gonadotropin (hCG)2.1 Biology
Human chorionic gonadotropin (hCG) is a heterodimeric glycoprotein produced predominantly by syncytiotrophoblast after implantation. Its alpha subunit is shared with LH, FSH, and TSH; the beta subunit provides much of the analytical specificity used in pregnancy testing.

• Serum hCG may become detectable approximately 8–10 days after ovulation, after implantation has begun, although timing varies.
• Concentrations rise rapidly during early pregnancy, generally peak near the end of the first trimester, then decline and remain at lower concentrations for the remainder of pregnancy.
• A single serum hCG measurement can establish that circulating hCG is detectable, but by itself it cannot determine pregnancy viability or location. Serial values and ultrasound are usually more informative when viability or pregnancy location is uncertain.

Thresholds are assay-dependent and should be interpreted using the laboratory’s own analytical specifications.

2.3 Serial hCG dynamics: why “doubling every 48 hours” is too simple
The traditional rule that hCG must “double every 48 hours” is an oversimplification.
Barnhart et al. (2004) studied 287 symptomatic patients who ultimately had viable intrauterine pregnancies and found that the slowest observed 48-hour rise within the study’s confidence limits was approximately 53%.
Later work showed that the minimum expected rise depends on the starting hCG concentration. In a viable intrauterine pregnancy, the lower-bound expected increase over approximately 48 hours is commonly summarized as follows:


A 35% rise over 48 hours has also been proposed in selected studies of pregnancy of unknown location (PUL) as a highly conservative lower bound designed to reduce the risk of misclassifying a potentially viable pregnancy. This 35% threshold is not an ACOG, SMFM, or NICE definition of a normal hCG rise, and it should not be interpreted as proof of normality, viability, or intrauterine location.
In UK/NICE-guided practice, NICE uses a specific management framework for pregnancy of unknown location (PUL):

• an hCG rise of >63% over 48 hours makes a developing intrauterine pregnancy likely;
• however, ectopic pregnancy still cannot be excluded;
• an increase of <63% or a fall of <50% requires prompt clinical review.

As gestation advances and hCG concentrations become higher, the rate of rise normally slows. There is no universal hCG concentration such as 6,000 mIU/mL at which hCG “plateaus.” Ultrasound becomes progressively more informative than repeated hCG measurements as the pregnancy develops.
Most importantly, no hCG pattern can by itself determine pregnancy location.

2.4 The discriminatory level: useful concept, dangerous shortcut
The “discriminatory level” is the serum hCG concentration above which an intrauterine gestational sac would be expected to be seen by transvaginal ultrasound in most viable pregnancies. It should be used cautiously.
Connolly et al. studied 651 symptomatic first-trimester pregnancies and estimated the hCG concentrations at which structures would be predicted to be visible 99% of the time:

• gestational sac: 3,510 mIU/mL
• yolk sac: 17,716 mIU/mL
• fetal pole: 47,685 mIU/mL

When a discriminatory level is used clinically, a conservative value around 3,500 mIU/mL for gestational-sac visualization reduces the risk of interrupting a potentially viable intrauterine pregnancy.
A high hCG level without an intrauterine sac does not by itself diagnose ectopic pregnancy. Symptoms, serial assessment, and repeat transvaginal ultrasound remain essential.
Urgent assessment is required for severe or worsening abdominal/pelvic pain, shoulder-tip pain, syncope, marked dizziness, hemodynamic instability, or heavy bleeding, regardless of the hCG value.

2.5 hCG “reference ranges” by week
Week-by-week hCG ranges overlap so extensively that universal tables can be misleading. Different laboratories, assays, populations, and methods produce different intervals.
For clinical interpretation:

1. use the laboratory’s own reference information;
2. interpret hCG relative to gestational timing and symptoms;
3. use serial change when clinically indicated; and
4. use ultrasound rather than hCG alone to assess pregnancy location and development.

A single hCG concentration should not be used to date a pregnancy or declare it viable or nonviable.

3. Screening for Fetal Aneuploidy: Serum-Based Screening
3.1 First-trimester combined screening
First-trimester combined screening uses:

• nuchal translucency (NT) ultrasound,
• maternal serum PAPP-A (pregnancy-associated plasma protein A), and
• free β-hCG,

together with maternal and pregnancy characteristics to estimate risk.
Current ACOG/SMFM guidance cites historically established detection rates for trisomy 21 with conventional first-trimester combined screening of approximately:

• 87% when performed at 11 weeks,
• 85% at 12 weeks, and
• 82% at 13 weeks,

with a screen-positive rate of about 5%. These estimates come from conventional nuchal-translucency-plus-serum screening programs and are lower than the performance achieved with cfDNA screening.
Low PAPP-A can also be associated with placental dysfunction and adverse pregnancy outcomes, but it is not independently diagnostic of placental disease.

3.2 Second-trimester quad screen
The quad screen usually measures:

• AFP (alpha-fetoprotein),
• hCG,
• unconjugated estriol (uE3), and
• dimeric inhibin A (DIA).

For trisomy 21, the classic serum pattern is:

• low AFP
• low uE3
• high hCG
• high inhibin A

The quad screen has lower screening performance for common aneuploidies than cfDNA.
Importantly, elevated — not low — maternal serum AFP raises concern for open neural-tube defects and can also be associated with abdominal-wall defects, incorrect gestational dating, multiple gestation, placental pathology, or other causes. An abnormal AFP result therefore requires clinical correlation and usually targeted ultrasound evaluation.

3.3 Integrated and serum-integrated screening
Integrated screening combines first- and second-trimester information into a single risk estimate. Serum-integrated screening uses serum markers without NT.
These approaches remain valid in selected settings but are used less frequently where cfDNA is readily available.
ACOG/SMFM advises patients who choose screening to use one coherent prenatal screening strategy, rather than multiple independent screening tests that can produce conflicting risk estimates.

4. Cell-Free DNA Screening (NIPT): The Most Sensitive and Specific Screening Test for Common Aneuploidies
Cell-free DNA screening analyzes placental cfDNA circulating in maternal plasma. Although commonly called “fetal DNA,” most of the pregnancy-associated cfDNA detected in maternal plasma originates from the placenta. This distinction matters because confined placental mosaicism can make a cfDNA result discordant with the fetal genotype.
Current ACOG/SMFM guidance recommends that cfDNA screening for trisomies 21, 18, and 13 be made routinely available to all obstetric patients and identifies cfDNA as the most sensitive and specific screening test for these common fetal aneuploidies.
Testing is generally performed from around 10 weeks of gestation, depending on the assay and local guidance.
The proportion of placental cfDNA within total maternal plasma cfDNA is called the fetal fraction. It varies with gestational age, maternal body size, placental biology, aneuploidy, sample quality, and assay. Laboratories use assay-specific minimum fetal-fraction or quality thresholds; there is no single universal cutoff that applies to every platform.

4.1 Performance
A large 2017 meta-analysis by Gil et al. reported the following pooled performance in singleton pregnancies:

For trisomy 13, the confidence interval around the detection estimate was much wider because the number of affected cases was considerably smaller.
These figures describe screening sensitivity/detection rate, not the probability that an individual positive result is truly affected.

4.2 Sensitivity is not the same as positive predictive value
A test can have very high sensitivity and specificity while still producing some false-positive results.
The positive predictive value (PPV) depends strongly on the pretest probability of the condition, including:

• maternal age,
• gestational context,
• ultrasound findings,
• the specific chromosome involved, and
• the prevalence of the condition in the tested population.

For that reason, there is no single universal PPV for “NIPT.”
A positive cfDNA result should be followed by genetic counseling, detailed ultrasound evaluation, and an offer of diagnostic testing with chorionic villus sampling (CVS) or amniocentesis before irreversible pregnancy-management decisions are made.

4.3 Why discordant and false-positive results occur
A major biological cause is confined placental mosaicism: the placenta contains a chromosomal abnormality that is absent from the fetus.
Other causes include:

• vanishing twin,
• maternal chromosome abnormalities or mosaicism,
• maternal copy-number variants,
• maternal malignancy in rare cases, and
• technical/sample factors.

This is why cfDNA remains a screening test, not a diagnostic test.

4.4 Sex-chromosome aneuploidies, microdeletions, and expanded cfDNA panels
Current SMFM guidance, endorsed by ACOG, distinguishes routine screening for the common autosomal trisomies from optional or non-routine uses of cfDNA:

• Sex-chromosome aneuploidy screening should be an opt-in consideration, offered only after appropriate pretest counseling rather than included automatically in every cfDNA panel.
• Routine general-population cfDNA screening for microdeletion syndromes is not recommended.
• Patients who choose cfDNA screening specifically for 22q11.2 deletion should do so only after appropriate pretest counseling.
• Patients who want information about the risk of broader fetal copy-number variants (CNVs) should be offered diagnostic testing rather than cfDNA microdeletion screening.
• Routine cfDNA screening for large genome-wide copy-number deletions or duplications is not recommended.

Commercial availability does not necessarily mean that a cfDNA target is recommended for routine population screening.

4.5 Twins and nonreportable results
The 2025 SMFM guidance endorsed by ACOG in 2026 recommends:

• cfDNA as a first-line screening option for trisomy 21 in twin gestations;
• cfDNA screening for trisomies 18 and 13 in twins, although the number of affected pregnancies studied is smaller;
• against routine cfDNA screening for sex-chromosome aneuploidy in twins because of insufficient evidence; and
• against cfDNA screening for higher-order multiples because of insufficient evidence.

A nonreportable / no-call cfDNA result is clinically important. Current ACOG/SMFM guidance recommends genetic counseling, comprehensive ultrasound evaluation, and offering diagnostic testing because nonreportable results can be associated with increased aneuploidy risk. Whether a repeat cfDNA sample is appropriate depends on the clinical situation, gestational age, and ultrasound findings.

4.6 What cfDNA does not replace
Regardless of which aneuploidy screening strategy is chosen, prenatal ultrasound remains necessary for fetal structural assessment. Current ACOG guidance recommends a second-trimester anatomic survey for all patients because structural abnormalities and some genetic conditions may occur with or without aneuploidy and may not be detected by cfDNA screening.

5. Beyond Chromosomes: Blood Tests for Pregnancy Complications5.1 Preeclampsia: angiogenic markers and emerging cfRNA
In some health systems, placental-growth-factor-based testing is used in patients with suspected preterm preeclampsia, not as universal screening.
In UK/NICE-guided settings, NICE recommends PLGF-based tests, including selected sFlt-1/PlGF ratio assays, together with standard clinical assessment for suspected preterm preeclampsia between 20+0 and 36+6 weeks.
Cell-free RNA: promising, but still investigational
cfRNA provides a dynamic view of gene-expression signals originating from maternal, placental, and fetal-associated tissues.

Key studies include:

• Ngo et al., Science 2018 — a pilot study showed that maternal plasma cfRNA signatures could estimate gestational age and identified a small transcript panel associated with spontaneous preterm delivery.
• Moufarrej et al., Nature 2022 — identified and independently validated an 18-gene cfRNA signature measured at 5–16 weeks that was associated with later preeclampsia.
• Zhou et al., AJOG 2023 — developed cfRNA-based classifiers for preterm and early-onset preeclampsia; models combining cfRNA features with clinical variables showed promising discrimination in validation cohorts.
• Castillo-Marco et al., Nature Communications 2025 — a first-trimester cfRNA model for early-onset preeclampsia achieved an AUC of approximately 0.88 in internal validation and 0.87 in an independent external validation dataset.

These findings support the presence of molecular changes well before clinical presentation, but cfRNA prediction is not yet a routine standard-of-care prenatal test. Larger independent validation, calibration across populations, assay standardization, clinical-utility studies, and regulatory evaluation remain necessary.

6. Routine and Commonly Indicated Maternal Blood Tests
6.1 Complete blood count and iron status
A complete blood count (CBC) is routinely used during pregnancy to assess hemoglobin, hematocrit, red-cell indices, platelets, and other parameters.
Pregnancy causes physiologic plasma-volume expansion, so hemoglobin and hematocrit normally fall to some degree. Diagnostic anemia thresholds vary by gestational stage and guideline.
Iron deficiency is common and should not be inferred from hemoglobin alone. Ferritin is the key laboratory marker of iron stores, interpreted in clinical context.
The 2026 ASH guideline on diagnosis of iron deficiency recommends:

• in pregnant individuals, serum ferritin ≤30 ng/mL as the diagnostic threshold for iron deficiency rather than the older ≤15 ng/mL threshold;
• in pregnant individuals with anemia, a threshold up to ≤50 ng/mL may be appropriate in selected clinical circumstances.

Inflammation can raise serum ferritin and make an isolated ferritin result more difficult to interpret. A ferritin value above 30 ng/mL does not by itself exclude iron deficiency when inflammation is present. In patients with inflammatory conditions or suspected inflammation, clinical context and, when appropriate, additional iron studies such as transferrin saturation may be needed.
Laboratory “normal ranges” and clinical diagnostic thresholds are not necessarily the same thing.

6.2 Blood group, RhD status, and red-cell antibodies
ABO/RhD typing and an antibody screen are generally performed early in prenatal care.
If a clinically significant maternal red-cell antibody is detected, follow-up depends on the antibody, titer/concentration, prior pregnancy history, and local fetal-medicine protocol.
RhD-negative, non-sensitized patients may require Rh immune globulin prophylaxis. Dose and timing vary internationally. In U.S. practice, a common regimen is 300 μg at approximately 28 weeks and postpartum when the newborn is RhD-positive, with additional prophylaxis after certain sensitizing events.

6.3 Gestational diabetes
Gestational-diabetes screening is generally performed at 24–28 weeks in patients without previously diagnosed diabetes, with earlier assessment in selected high-risk situations.
Two widely used strategies are:
One-step approach

• fasting 75-g OGTT
• glucose measured fasting, at 1 hour, and at 2 hours

Two-step approach

1. nonfasting 50-g glucose load test (GLT);
2. if screen-positive, fasting 100-g 3-hour OGTT.

A 50-g screen followed by a 75-g OGTT is not the standard two-step strategy described by ADA/ACOG.
HbA1c may be useful in selected contexts for identifying pre-existing dysglycemia early in pregnancy, but it is not a substitute for the standard 24–28-week GDM testing strategy.

6.4 Infectious-disease screening
Recommended prenatal infectious-disease testing varies by jurisdiction.
In U.S. guidance, routine screening includes, among other tests:

• HIV
• syphilis
• hepatitis B
• hepatitis C during each pregnancy
• assessment of rubella immunity

Additional testing is based on geography, exposure, symptoms, local prevalence, and individual risk.

6.5 Thyroid and vitamin D testing
Universal TSH screening is not uniformly recommended. Thyroid testing is appropriate when symptoms, history, risk factors, medication use, or local policy indicate it.
Likewise, routine 25-hydroxyvitamin D screening for every pregnant patient is not supported by current ACOG guidance. Testing can be considered in individuals at increased risk of deficiency.

7. Test Timeline at a Glance
This timeline is illustrative. Local prenatal-care protocols differ.


Important: ACOG/SMFM advises against performing multiple independent aneuploidy screening strategies at the same time simply to “double check,” because this can increase discordant or false-positive results.


8. Interpretation Pitfalls Every Reader Should Know
8.1 The high-dose hook effect
At extremely high hCG concentrations, some sandwich immunoassays can become saturated and produce a falsely low result. This is uncommon and assay-dependent, but it should be considered when the clinical picture strongly conflicts with the laboratory result, particularly in gestational trophoblastic disease.

8.2 Heterophile antibodies and biotin
Heterophile antibodies can produce spurious immunoassay results.
High-dose biotin can also interfere with assays that use streptavidin-biotin technology. The direction of error depends on assay design:

• sandwich assays may read falsely low;
• competitive assays may read falsely high.

For thyroid testing, this can produce patterns such as falsely low TSH with falsely high free thyroid hormones on susceptible platforms.
Patients should tell the laboratory and clinician about high-dose biotin or other supplements when results do not fit the clinical picture.

8.3 Gestational trophoblastic disease
Markedly abnormal, persistently elevated, or plateauing hCG in the appropriate clinical setting can occur with gestational trophoblastic disease or neoplasia and requires specialist assessment.
8.4 Pregnancy of unknown location
A PUL means a positive pregnancy test with no definite intrauterine or ectopic pregnancy identified on ultrasound.

• hCG should not be used alone to determine pregnancy location.
• Symptoms take priority over the hCG trend.
• Serial hCG and repeat ultrasound guide management.
• NICE specifically advises against using serum progesterone as an adjunct to diagnose viable intrauterine pregnancy versus ectopic pregnancy in PUL.

8.5 NIPT is screening, not diagnosis
A high-risk cfDNA result should not be treated as a definitive fetal diagnosis. Diagnostic testing with CVS or amniocentesis should be offered before irreversible management decisions.

8.6 Assay and laboratory variability
Reference intervals, calibration, analytical sensitivity, interference, and reporting conventions differ across laboratories.
When serial measurements are being interpreted clinically, using the same laboratory and assay platform is preferable when practical.

CVS samples placental tissue, whereas amniocentesis samples amniotic fluid containing fetal cells. Confined placental mosaicism can therefore occasionally complicate CVS interpretation and may require additional evaluation.
The procedure-related pregnancy-loss risk with modern CVS and amniocentesis is low but not zero and depends on clinical circumstances, operator experience, and how background pregnancy loss is estimated.

10. The Next Decade: AI and Multi-Omics Interpretation
Prominent research directions include:

1. Multi-analyte and multi-omic models — combining cfDNA, cfRNA, proteins, metabolites, conventional laboratory results, and clinical variables.
2. Longitudinal interpretation — modeling changes across gestation rather than comparing one result with a static population cutoff.
3. Machine-learning-assisted risk estimation — integrating gestational age, prior measurements, comorbidities, and multiple biomarkers.
4. Earlier prediction windows — identifying biological changes before conventional clinical signs appear.

These approaches are promising, but predictive performance alone is not enough for clinical adoption. Models require:

• external and prospective validation,
• calibration in the intended population,
• assessment of bias and subgroup performance,
• evidence that using the model improves clinical outcomes,
• transparent handling of uncertainty, and
• appropriate regulatory and data-governance frameworks.

For patients and clinicians, the practical message is already clear: laboratory results increasingly require contextual interpretation. A ferritin result should be interpreted against clinical diagnostic thresholds rather than a laboratory reference interval alone; a cfDNA result requires understanding of pretest probability, fetal fraction/quality metrics, and whether the result is screening or diagnostic.


11. Frequently Asked Questions
How early can a blood test detect pregnancy?
Serum hCG may become detectable approximately 8–10 days after ovulation in some pregnancies, after implantation has started. A negative result very early does not exclude pregnancy because implantation and hCG production vary between individuals.
Is a blood pregnancy test more accurate than a urine test?
Serum testing is generally more analytically sensitive, can detect lower hCG concentrations, and can provide a quantitative result. Modern urine tests can be highly accurate when used at the appropriate time, especially after a missed period.
What hCG level confirms a viable pregnancy?
No single hCG concentration confirms viability. Serial change, symptoms, gestational timing, and ultrasound findings must be interpreted together.
Does a normal hCG rise rule out ectopic pregnancy?
No. An ectopic pregnancy can sometimes show an apparently appropriate hCG rise. Pregnancy location is determined through clinical assessment and imaging, not hCG alone.
If NIPT is “99% accurate,” why must positive results be confirmed?
Because sensitivity is not the same as PPV. Even a highly sensitive and specific screening test can produce false positives, particularly when the condition being screened for is uncommon. Placental mosaicism and other biological factors can also cause discordant results.
What does a ferritin of 20 ng/mL mean in pregnancy?
Under the 2026 ASH guideline, ferritin ≤30 ng/mL in pregnancy supports a diagnosis of iron deficiency, regardless of whether the laboratory’s printed reference interval labels the value as “normal.” Inflammation can raise ferritin, so a value above 30 ng/mL does not always exclude iron deficiency; clinical context and, when appropriate, additional iron studies still matter.
Which blood tests are routinely recommended during pregnancy?
The exact schedule varies by country, but routine prenatal care commonly includes CBC, ABO/RhD typing, red-cell antibody screening, selected infectious-disease testing, and gestational-diabetes screening. Other tests — including thyroid studies, vitamin D, serial hCG, angiogenic markers, and genetic screening — depend on timing, clinical indication, patient preference, and local guidance.


Prepared by: Aima Diagnostics Editorial Team
Evidence reviewed through: September 2026
Last updated: September 24, 2026


References

1. American College of Obstetricians and Gynecologists (ACOG). Screening for Fetal Chromosomal Abnormalities. Practice Advisory. January 2026. This guidance endorses SMFM Consult Series #74 and replaces ACOG Practice Bulletin No. 226 for current aneuploidy-screening guidance.
2. Rink BD, Dugoff L, Kuller JA. Society for Maternal-Fetal Medicine Consult Series #74: Cell-free DNA screening for aneuploidies: updated guidance. Pregnancy. 2025;1. doi:10.1002/pmf2.70139.
3. National Institute for Health and Care Excellence (NICE). NG126: Ectopic pregnancy and miscarriage: diagnosis and initial management. Published 2019; updated 17 June 2026.
4. American College of Obstetricians and Gynecologists. Practice Bulletin No. 193: Tubal Ectopic Pregnancy. Obstet Gynecol. 2018;131–e103.
5. Barnhart KT, Sammel MD, Rinaudo PF, Zhou L, Hummel AC, Guo W. Symptomatic patients with an early viable intrauterine pregnancy: HCG curves redefined. Obstet Gynecol. 2004;104(1):50–55. doi:10.1097/01.AOG.0000128174.48843.12.
6. Barnhart KT, Guo W, Cary MS, et al. Differences in serum human chorionic gonadotropin rise in early pregnancy by race and value at presentation. Obstet Gynecol. 2016;128(3):504–511. doi:10.1097/AOG.0000000000001568.
7. Connolly A, Ryan DH, Stuebe AM, Wolfe HM. Reevaluation of discriminatory and threshold levels for serum β-hCG in early pregnancy. Obstet Gynecol. 2013;121(1):65–70. doi:10.1097/AOG.0b013e318278f421.
8. Taylor-Phillips S, Freeman K, Geppert J, et al. Accuracy of non-invasive prenatal testing using cell-free DNA for detection of Down, Edwards and Patau syndromes: a systematic review and meta-analysis. BMJ Open. 2016;6. doi:10.1136/bmjopen-2015-010002.
9. Gil MM, Accurti V, Santacruz B, Plana MN, Nicolaides KH. Analysis of cell-free DNA in maternal blood in screening for aneuploidies: updated meta-analysis. Ultrasound Obstet Gynecol. 2017;50(3):302–314. doi:10.1002/uog.17484.
10. Dar P, Jacobsson B, MacPherson C, et al. Cell-free DNA screening for trisomies 21, 18, and 13 in pregnancies at low and high risk for aneuploidy with genetic confirmation. Am J Obstet Gynecol. 2022;227(2):259.e1–259.e14. doi:10.1016/j.ajog.2022.01.019.
11. Khalil A, Archer R, Hutchinson V, et al. Noninvasive prenatal screening in twin pregnancies with cell-free DNA using the IONA test: a prospective multicenter study. Am J Obstet Gynecol. 2021;225(1):79.e1–79.e13. doi:10.1016/j.ajog.2021.01.005.
12. National Institute for Health and Care Excellence (NICE). HTG630: PLGF-based testing to help diagnose suspected preterm pre-eclampsia. 2022.
13. Ngo TTM, Moufarrej MN, Rasmussen MLH, et al. Noninvasive blood tests for fetal development predict gestational age and preterm delivery. Science. 2018;360(6393):1133–1136. doi:10.1126/science.aar3819.
14. Moufarrej MN, Vorperian SK, Wong RJ, et al. Early prediction of preeclampsia in pregnancy with cell-free RNA. Nature. 2022;602:689–694. doi:10.1038/s41586-022-04410-z.
15. Zhou S, Li J, Yang W, et al. Noninvasive preeclampsia prediction using plasma cell-free RNA signatures. Am J Obstet Gynecol. 2023;229(5):553.e1–553.e16. doi:10.1016/j.ajog.2023.05.015.
16. Castillo-Marco N, Cordero T, Igual M, et al. Maternal plasma cell-free RNA as a predictor of early and late-onset preeclampsia throughout pregnancy. Nat Commun. 2025;16:9208. doi:10.1038/s41467-025-64215-2.
17. Powers JM, Lim MY, Achebe MO, et al. American Society of Hematology 2026 guidelines for diagnosis of iron deficiency. Blood Advances. 2026. doi:10.1182/bloodadvances.2025015950.
18. American Diabetes Association. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1).
19. Centers for Disease Control and Prevention. Clinical Screening and Diagnosis for Hepatitis C. Current guidance recommends hepatitis C screening during each pregnancy.
20. American College of Obstetricians and Gynecologists. Routine Tests During Pregnancy. Patient guidance.
21. American College of Obstetricians and Gynecologists. Prepregnancy Counseling. Committee Opinion No. 762. Obstet Gynecol. 2019.
22. American College of Obstetricians and Gynecologists. Vitamin D: Screening and Supplementation During Pregnancy. Committee Opinion No. 495.

This article is for educational purposes and does not replace individualized medical advice. Laboratory results should be interpreted by a qualified healthcare professional in the context of gestational age, symptoms, medical history, examination findings, ultrasound, assay characteristics, and local clinical guidance.

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