Evidence-based summary of initial visit evaluation and laboratory panel, adaptation of visit schedule, aneuploidy screening (cfDNA/NIPT, combined and quadruple testing), screening-diagnostic differentiation, and trimester-based routine screening program.
⚕️ Target audience: This clinical review is intended for physicians and healthcare professionals; It is a summary of current literature and guidelines for educational purposes. Clinical decisions should be made based on patient-specific evaluation and applicable institutional protocols.
Prenatal care; It is a coordinated monitoring process consisting of three basic components: risk assessment, health promotion/education and therapeutic intervention, aiming to prevent pregnancy complications or to recognize and treat them in a timely manner (UpToDate, "Prenatal care: Initial assessment", 2026). The primary goal is the birth of a healthy newborn by minimizing maternal risk; Its components include early and accurate estimation of gestational age, detection of high-risk pregnancies, continuous monitoring of maternal-fetal health, prediction of problems and provision of respectful maternity care.
Pregnancy and childbirth complications are the leading cause of morbidity and mortality in women of reproductive age globally. In the US, among pregnancies resulting in live birth in 2024, prenatal care began in the first trimester for approximately 76%, in the second trimester for 17%, and in the third trimester or not at all for 7% (UpToDate 2026, US national data). The World Health Organization (WHO) states that approximately 60% of pregnant women begin antenatal care before the 12th week; However, it reports that there are significant inequalities based on income and region.
The effectiveness of some components of antenatal care is supported by randomized data: midwife-led continuity models reduce cesarean section (RR 0.91, 95% CI 0.84-0.99) and increase spontaneous vaginal birth; whereas, particularly in low/middle-income countries, extremely reduced number of visits (usually <5 visits) increased perinatal mortality (RR 1.15, 95% CI 1.01-1.32) (Cochrane systematic reviews; UpToDate 2026).
Prenatal care should begin in the first trimester, ideally by 10 weeks of gestation (≤10 0/7 weeks), because some screening and diagnostic tests can be performed from 10–11 weeks onward. Early initiation allows accurate gestational dating, baseline measurements in patients with chronic disease, and early social support (UpToDate 2026).
History should include demographic information, past obstetric history (complications in previous pregnancies increase risk in subsequent pregnancies), medical and surgical history, medication use, allergies and immunization status, assessment of hereditary disease and substance-use risks, infection exposure, and psychosocial history (whether the pregnancy was planned, barriers to care, mental health, food and housing security, and intimate partner violence). ACOG recommends using validated tools such as the PHQ-9 or Edinburgh Postnatal Depression Scale for depression and anxiety screening at the first visit and thereafter; bipolar disorder screening should be performed before starting pharmacotherapy.
During physical examination, basal blood pressure, weight and height are recorded; Body mass index (BMI) is calculated and counseling is given for appropriate gestational weight gain. If initial blood pressure is high, pre-pregnancy values should be investigated to distinguish chronic hypertension (chronic HT: ≥140/90 mmHg before the 20th week). Uterine size and adnexa are evaluated; Early ultrasound is indicated in case of size-menstrual date discrepancy. Fetal heart activity is usually heard with hand Doppler in the 12th week (fetal cardiac movement can be detected in the 5.5th week with transvaginal ultrasonography).
First trimester ultrasonography determines gestational age more accurately than the last menstrual period; It reduces the frequency of induction for postterm pregnancy and tocolysis for suspected preterm labor. It also provides early detection of multiple pregnancy, determination of chorionicity/amnionicity and evaluation of early anatomical markers associated with aneuploidy (UpToDate 2026). Sonographic dating before the 20th week is recommended in all pregnancies.
ACOG's standard prenatal laboratory panel is administered to each new obstetric patient at the first visit. Urine culture for asymptomatic bacteriuria is recommended by ACOG and USPSTF to prevent pyelonephritis in early pregnancy.
| Test | Purpose / clinical use |
|---|---|
| Complete blood count (CBC) | Anemia, thrombocytopenia; Preliminary screening for hemoglobinopathy/iron deficiency with MCV |
| Blood type, Rh(D) and indirect Coombs (antibody screening) | Rh(D) isoimmunization risk and anti-D prophylaxis planning; alloantibody detection |
| Rubella IgG | Immune status; Postpartum vaccination plan in non-immune patient |
| HBsAg (Hepatitis B surface antigen) | Requirement for immunoprophylaxis (HBIG + vaccine) in the newborn |
| HIV (Ag/Ab combined immunoassay) | Antiretroviral therapy to prevent perinatal transmission; "opt-out" screening |
| Syphilis serology (treponemal/non-treponemal) | Prevention of congenital syphilis; treatment during pregnancy |
| Urine culture | Screening for asymptomatic bacteriuria (prevention of pyelonephritis/preterm birth) |
| Hepatitis C (HCV) antibody | Universal screening in every pregnancy (current CDC/ACOG) |
| Carrier screening (cystic fibrosis, SMA; hemoglobinopathies) | Pan-ethnic or expanded carrier screening; inherited disease risk |
| Thyroid, fasting glucose/HbA1c, cervical cytology | Based on indication and age/risk; Screening for overt diabetes in early pregnancy in selected patients |
In the USA, typical visit intervals for a low-risk nulliparous pregnant woman are every 4 weeks until week 28, every 2 weeks between weeks 28 and 36, and then weekly until birth; With this scheme, a total of 12-14 visits occur in a pregnant woman whose first visit is ≤10 weeks and the last visit is term (UpToDate, "Prenatal care: Second and third trimesters", 2026). However, the superiority of this fixed scheme, which has remained largely unchanged for nearly a century, has not been proven with randomized data; The 2022 AHRQ review and 2023 meta-analysis found no significant differences in gestational age, SGA, NICU admission, and low Apgar between reduced (6-10 visits) and standard (12-15 visits) programs.
Based on this evidence, in Clinical Consensus No. 8, "Tailored Prenatal Care Delivery for Pregnant Individuals" (May 2025), ACOG proposed a fundamental redesign of prenatal care delivery for the first time in nearly a century. The consensus provides guidance in three areas: (1) addressing unmet social needs, (2) individualizing visit frequency and surveillance according to medical and social risk, and (3) integrating telehealth and alternative care modalities. While low-risk pregnant patients may be followed with fewer in-person visits, group prenatal care, or telehealth visits, high-risk patients require more frequent visits tailored to their condition.
International guidelines recommend different schemes: NICE NG201 (2021) 11 appointments (including first appointment) for nulliparous pregnant women, 9 appointments for multiparous; WHO recommends a minimum of 8 antenatal contacts (1 in the first, 2 in the second and 5 in the third trimester), regardless of parity. The COVID-19 pandemic has demonstrated that telehealth supported by home devices can be safely and effectively integrated into routine prenatal care and is particularly helpful for pregnant women with perinatal mood disorders, diabetes, or hypertension (UpToDate 2026).
Screening tests should be performed early in the recommended intervals to allow sufficient time for counseling and diagnostic testing when necessary. The table below summarizes the routine screening schedule in a singleton low-risk pregnancy; The details of each test are discussed on the relevant pages.
| Week of pregnancy | Screening / procedure | Note |
|---|---|---|
| First visit (<10 weeks ideal) | Standard laboratory panel (Table 1); dating USG; aneuploidy/carrier screening counseling | Early start critical for gestational age accuracy and timing of intervention |
| 10-13 6/7 weeks | cfDNA (NIPT) or first trimester combined test (NT + PAPP-A + free β-hCG) | Blood for cfDNA is collected at ≥9-10 weeks; CVS should be accessible with combined testing |
| 15-22 6/7 weeks | Quadruple test (if not screened in the first trimester); Neural tube defect screening with MSAFP/USG | Ideal MSAFP 16-18 weeks; quadruple testing also screens for open NTD |
| 16-24 weeks | Transvaginal USG for short cervix (≤25 mm) | Can be measured during anomaly scanning; risk of preterm birth |
| 18-22 weeks | Fetal anatomy (anomaly) scan | Sensitivity higher in the second trimester — anomaly screening page (anomaly scan page) |
| 24-28 weeks | Gestational diabetes (GDM) screening: one-step 75 g or two-step 50 g→100 g | Universal scan; selective approach less effective |
| 28 weeks | Repeat antibody screening + anti-D immunoglobulin in D-negative pregnant woman; Hb/Htc for anemia | Anemia thresholds: 1st/3rd. trim <11, 2nd trim <10.5 g/dL |
| 28-36 weeks | STI screening in high-risk pregnant women (HIV, syphilis, chlamydia, gonorrhea) | CDC; community/risk based |
| 36 0/7-37 6/7 weeks | Group B Streptococcus (GBS) vaginal-rectal culture | For intrapartum prophylaxis plan |
Each of these screening steps is the subject of a separate clinical review: gestational diabetes, anemia in pregnancy, GBS and intrapartum prophylaxis, and Rh(D) isoimmunization and anti-D prophylaxis. Blood pressure, weight, fundal height, and fetal heart rate are also assessed at each visit; these simple, inexpensive measurements detect 20–50% of growth abnormalities, prevent approximately 70% of eclampsia through early diagnosis of preeclampsia, and identify 80% of breech presentations before birth (UpToDate 2026).
Current guidelines recommend that aneuploidy screening be offered to all pregnant women, regardless of maternal age; It also recommends that every pregnant woman, regardless of age, have the option of skipping screening and going directly to diagnostic testing (an invasive procedure) (ACOG; UpToDate 2026). The most critical concept here is the distinction between screening and diagnosis: screening tests only determine risk (high/low probability of aneuploidy), not diagnosis; Definitive diagnosis requires fetal/placental cell sampling (chorion villus sampling [CVS] or amniocentesis). A screen-negative result does not exclude aneuploidy; a scan-positive result does not prove aneuploidy. The term "normal" should not be used for the patient; the meaning of a positive/negative result, the possibility of a false positive/negative, and possible further testing should be explained to the patient.
Evaluation of cell-free DNA (cfDNA) in maternal blood by next-generation sequencing has become the most common aneuploidy screening method. The major source of “fetal” cfDNA in the maternal circulation is the apoptosis of placental syncytiotrophoblast cells; therefore the test actually reflects the placental genotype, and placenta-fetus incompatibility (mosaicism) is the source of false results. Although cfDNA can be detected from week 5 onwards, for an adequate fetal fraction (usually at least 3.5%), most laboratories take the blood sample at ≥9–10 weeks. Maternal obesity, IVF pregnancy, twin pregnancy and use of low molecular weight heparin before the 20th week reduce the fetal fraction, increasing the risk of "no-call" (~1-3% in the general population; much higher in advanced obesity) (UpToDate, "...Cell-free DNA testing", 2025).
cfDNA detects approximately 99% of trisomy 21 cases; estimated values derived from meta-analyses are summarized in the table below. Every patient with a positive result should be offered an invasive procedure for definitive diagnosis, because although the positive predictive value (PPV) for trisomy 21 in the general obstetric population is ≥85%, it is not 100%—the combined PPV of the three common trisomies is approximately 73% in the general population. The negative predictive value is very high at ≥99.9% for all trisomies (UpToDate 2025). cfDNA does not provide a risk estimate for open neural tube defects; therefore, NTD screening with MSAFP or USG in the second trimester should be offered separately.
Important guidance update: cfDNA screening guidance ACOG Practice Bulletin No. 226 (October 2020) revealed that cfDNA could be a first-line screening option in all patients, regardless of maternal age or baseline risk. This document has now been superseded by SMFM Consult Series #74 (2025, “cfDNA screening for aneuploidies: Updated guidance”) and its companion ACOG Practice Advisory (January 2026) (ACOG approved #74 in November 2025). Current guidance; It provides renewed information on the use of cfDNA in sex chromosome aneuploidies and microdeletions and its application in multiple pregnancies.
The use of biochemical marker-based tests is decreasing due to the higher sensitivity and specificity of cfDNA; however, these tests remain valuable in open NTD screening (those containing AFP) and in situations where access to cfDNA is limited (UpToDate, "Down syndrome: Overview of prenatal screening", 2025). The first-trimester combined test combines nuchal translucency (NT) measurement with PAPP-A (decreased in Down syndrome) and free β/total hCG (increased approximately twofold) levels; in most patients, it is performed at 11 0/7-13 6/7 weeks. The second-trimester quadruple test (Quad) measures AFP, unconjugated estriol (uE3), hCG, and dimeric inhibin A; it is ideally performed at 15 0/7-18 6/7 weeks (22 6/7 at the latest) and also screens for open NTDs, but does not detect trisomy 13. Multiple screening tests should not be performed simultaneously.
| Test | Timing | Trisomy 21 detection (false positive) | Important features |
|---|---|---|---|
| cfDNA (NIPT) | ≥9-10 weeks | T21 ~99% (DR 99.5%; FPR 0.05%) T18 DR 97.7%; T13 DR 96.1% | Highest DR/lowest FPR; sex chromosome aneuploidies ± microdeletion; does not screen for open NTD; ~1-3% no-call; If positive, invasive diagnosis is required |
| First trimester combined test | 11 0/7-13 6/7 weeks | ~82–87% (FPR 5%) | NT + PAPP-A + free β-hCG; early; positive requires CVS access; NTD screening should be added in the second trimester |
| Second trimester quadruple test (Quad) | 15 0/7-22 6/7 weeks | ~81% (FPR 5%) | AFP, uE3, hCG, inhibin A; also scans for open NTD; does not detect trisomy 13 |
| Fully integrated testing | 1st tri (NT+PAPP-A) + 2nd tri Quad | Lowest FPR at high DR | For patients who prioritize high detection over first trimester diagnosis; scans for open NTD |
NT-only measurement or single-marker approaches show lower performance (NT alone ~64-70%). cfDNA may be offered as a secondary screen in a biochemical screen-positive patient; Due to its high specificity, most initial false positives are reclassified as screen-negative (minimal risk of misclassification). Risk communication is difficult: in one study, patients informed with a “1/150” format perceived the risk to be higher than those who heard the same risk with a “7/1000” format — visual aids are useful (UpToDate 2025).
Diagnostic genetic testing is a reasonable choice for high-risk pregnant women of any age: in the presence of a screen-positive result, a previous trisomy pregnancy, at least one major or two minor structural anomalies in the current pregnancy, or a balanced translocation/inversion in the parent. Chorionic villus sampling (CVS) is performed in the first trimester and amniocentesis in the second trimester; Karyotype or chromosomal microarray (CMA) is obtained from the samples. In experienced high-volume centers, the procedure-related pregnancy loss rate is estimated to be approximately 0.1-0.3% (1/300-1/1000) for both; The higher observed loss rate in CVS is associated with an earlier gestational week and a higher risk of baseline loss at that time (UpToDate 2025). Rapid (interphase) diagnosis is possible with FISH or QF-PCR; if normal, full karyotype/CMA is usually completed anyway. If the cfDNA result suggests the possibility of placental mosaicism, CVS may not be preferred.
An anatomy scan is ideally performed at 18–22 weeks; Although many anomalies can be seen in the first trimester, sensitivity is higher in the second trimester (for details, 20-22 week anomaly scan). This window is optimal because Down syndrome fetuses are at increased risk for congenital heart anomalies and duodenal atresia. (20-22 weeks anomaly scan)
Maternal immunization is an essential component of prenatal care (ACOG maternal immunization guideline, updated February 2026): Tdap is recommended in every pregnancy at 27–36 weeks (as early as possible); inactivated influenza and COVID-19 vaccines can be given in any trimester; RSVpreF (Abrysvo) is given seasonally at 32 0/7–36 6/7 weeks to prevent RSV lower respiratory tract infection in the infant. See the pregnancy vaccination guide for the timing and rationale. (guide to vaccinations during pregnancy)
Nutrition and folic acid: 0.4-0.8 mg (400-800 mcg) folic acid daily is recommended for all individuals who are planning pregnancy or may become pregnant (USPSTF 2023). In high-risk groups, such as previous pregnancies with neural tube defects, the dose is increased to 4 mg daily, ideally starting ~3 months before conception and continuing until the 12th week of gestation (ACOG/AAFP). Balanced energy/protein supplementation has been implicated among interventions that reduce the risk of stillbirth in low-income settings.
Number of visits. The superiority of the nearly century-old traditional 12-14 visit schedule is not supported by randomized evidence; ACOG Clinical Consensus No. 8 (2025) and telehealth data support individualized models with fewer face-to-face visits in low-risk pregnancies. In contrast, as over-reduction increases perinatal mortality (RR 1.15), particularly in low/middle-income countries, “reduction” should be made sensitive to context and satisfaction monitored as patients often find longer intervals “too long” (UpToDate 2026).
Sex chromosome aneuploidies and microdeletions. As cfDNA panels expand, the false positive rate increases and PPV decreases; for example, the combined PPV for sex chromosome aneuploidies is only ~37% in some studies. Therefore, specific pre-test counseling and consent are required for these targets; The current SMFM #74 / ACOG 2026 Advisory clarifies these uses.
Incidental maternal cancer. An abnormal/uninterpretable cfDNA pattern may rarely indicate maternal malignancy; however, cfDNA is not a cancer screening test and the clinical management of these findings has not yet been standardized (UpToDate 2025; IDENTIFY study is ongoing). Counseling should include this possibility.
Hemoglobinopathy screening. Although selective screening based on red blood cell indices has traditionally been used in the United States, increasing ethnic diversity means that universal (pan-ethnic) screening is increasingly preferred because it identifies more carriers.
ACOG Clinical Consensus No. 8 (2025), SMFM Consult Series #74 (2025) and cfDNA performance data are in effect as of 2024-2026. During this period, three concrete changes in screening protocols and a guideline citation correction stand out.
With its April 2024 Practice Advisory, ACOG abandoned risk-based third trimester screening and moved to recommending universal serological syphilis screening for all pregnant women at 3 time points: first prenatal visit, third trimester, and delivery. The rationale is that congenital syphilis in the United States has reached a 30-year high—3,882 cases and 279 stillbirths/neonatal-infant deaths in 2023 (ACOG Practice Advisory, April 2024). The USPSTF also reaffirmed “early, universal” screening with high certainty (“A” recommendation) in its 2025 reaffirmation; recommends screening at the first opportunity if not screened early (USPSTF, JAMA 2025;333:2006-2012; PMID 40358930). The two organizations are aligned in framework: USPSTF emphasizes early-universal entry, ACOG additionally emphasizes third trimester + re-screening at birth. Practical result: Syphilis screening at 28–36 weeks is now performed regardless of risk.
ACOG's March 2024 Practice Advisory on the RhIg (RhoGAM) national shortage in 2023-2024 recognized determination of fetal RHD status by NIPT/cfDNA as a reasonable approach to prioritize anti-D under shortage conditions. Approximately 40% of RhD-negative pregnant women carry an RhD-negative fetus; Antepartum anti-D is unnecessary if the fetus turns out to be RhD-negative (Moise KJ, AJOG 2025;232:188-193; PMID 39153534). NGS-based cfDNA testing had a sensitivity of 100% (95% CI 98.9-100) and specificity of 99.3% (95% CI 97.6-99.8) in a large US cohort (n=655); No false-negatives were detected at ≥9 weeks (Obstet Gynecol 2025;145:211-216; PMID 39591628). This strategy, which has been routine for years in Europe and Scandinavia, is not yet the universal standard in the United States — the ACOG context is specific to the shortage; It should not be presented as a standard recommendation.
Attribution correction: SMFM #74 supersedes SMFM Consult Series #36 (2015), not ACOG Practice Bulletin 226. The current ACOG basis for PB 226 (2020) is the January 2026 “Screening for Fetal Chromosomal Abnormalities” Practice Advisory; Operates with #74 (ACOG approval November 2025).
Timing of maternal immunization unchanged: ACOG August 2025 update reiterates recommendations for influenza, COVID-19, RSVpreF (Abrysvo; 32 0/7-36 6/7 weeks, seasonal), and Tdap (ACOG, August 2025).
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