Prenatal Care for the FNP Exam: Visit Schedule, Labs by Trimester and the Numbers to Know

Prenatal care questions on the FNP exam are calendar questions: which test belongs to which gestational age, and what number turns a screen positive. The traditional schedule is a visit every 4 weeks until 28 weeks, every 2 weeks from 28 to 36 weeks and weekly from 36 weeks until delivery. The anchor labs are a full panel at the first visit, glucose screening plus a repeat CBC and antibody screen at 24 to 28 weeks, Rh immune globulin at 28 weeks for Rh-negative unsensitized patients, and group B streptococcus (GBS) culture at 36 0/7 to 37 6/7 weeks. ACOG's 2025 Clinical Consensus on tailored prenatal care keeps those services but lets the provider adjust the number and format of visits, including telehealth, to each patient's medical and social needs.

The visit schedule

ACOG's 2025 consensus describes a risk and needs assessment at the first visit (medical, social and structural factors), a shared care plan, and then visit frequency and format tailored to that plan. Patients with chronic hypertension, diabetes or other high-risk conditions get more frequent visits and home monitoring; low-risk patients may have fewer in-person visits. Services that require hands-on care, such as laboratory draws, ultrasound and vaccines, still need to be scheduled at the right gestational age.

Dating the pregnancy

The estimated due date uses the first day of the last menstrual period plus 280 days (Naegele: add 7 days, subtract 3 months, add 1 year). A first-trimester ultrasound measuring crown-rump length is the most accurate dating method, and when it differs from menstrual dating by more than the accepted margin for that gestational age, the ultrasound date is used. Once set, the due date should not be changed by later ultrasounds.

Bedside measurements

• Fundal height reaches the umbilicus at about 20 weeks; from 20 to about 36 weeks the measurement in centimeters roughly equals the gestational age in weeks. A difference of more than about 2 to 3 cm calls for ultrasound for growth and fluid.
• Blood pressure at every visit is itself a USPSTF screening recommendation for preeclampsia.
• Weight gain targets follow the National Academy of Medicine ranges by prepregnancy BMI: 28 to 40 lb if underweight, 25 to 35 lb if normal weight, 15 to 25 lb if overweight and 11 to 20 lb with obesity.

First-visit laboratory panel

In addition, every patient is offered aneuploidy screening or diagnostic testing regardless of age, and carrier screening (for example cystic fibrosis, spinal muscular atrophy and hemoglobinopathies). Folic acid 0.4 to 0.8 mg daily continues through the first trimester; patients with a prior neural tube defect pregnancy take a higher prescribed dose. Tuberculosis testing is based on risk.

Early glucose screening

Routine screening is at 24 to 28 weeks. ACOG recommends earlier testing for patients with BMI 25 or higher (23 or higher for Asian American patients) plus at least one additional risk factor: physical inactivity, a first-degree relative with diabetes, high-risk race or ethnicity, prior gestational diabetes, a prior infant weighing 4,000 g or more, hypertension, HDL under 35 mg/dL or triglycerides over 250 mg/dL, polycystic ovary syndrome, an A1c of 5.7 percent or higher, or a history of cardiovascular disease. A negative early test is repeated at 24 to 28 weeks.

Aspirin for preeclampsia prevention

The USPSTF recommends low-dose aspirin (81 mg daily) after 12 weeks for patients at high risk of preeclampsia. High-risk features are a history of preeclampsia, multifetal gestation, chronic hypertension, pregestational diabetes, kidney disease or autoimmune disease such as lupus or antiphospholipid syndrome. Aspirin is also considered for patients with more than one moderate-risk factor, such as nulliparity, obesity, age 35 or older, a family history of preeclampsia, IVF conception or low income. ACOG advises starting between 12 and 28 weeks, ideally before 16 weeks, and continuing until delivery.

Second trimester

• Anatomy ultrasound at about 18 to 22 weeks.
• Maternal serum alpha-fetoprotein for open neural tube defects, typically at 15 to 22 weeks, when only first-trimester or cell-free DNA aneuploidy screening was done.
• Quickening (first fetal movements) at about 18 to 20 weeks in a first pregnancy, earlier in later pregnancies.

24 to 28 weeks: the busiest window

Gestational diabetes testing

ACOG Practice Bulletin 190 accepts both approaches, and the USPSTF recommends screening at 24 weeks or later.

Treatment begins with nutrition therapy and exercise. When glucose targets are not met, insulin is the preferred first medication in ACOG guidance. Patients with gestational diabetes need a 75 g 2-hour glucose tolerance test 4 to 12 weeks postpartum and lifelong diabetes screening afterward.

Other 24 to 28 week items

• Repeat CBC.
• Repeat antibody screen in Rh-negative patients, then Rh immune globulin at 28 weeks.
• Syphilis rescreen around 28 weeks.
• Tdap between 27 and 36 weeks in every pregnancy, preferably early in that window.
• Influenza vaccine in any trimester during the season. RSV vaccine is an option at 32 to 36 weeks in season, as an alternative to giving the infant a monoclonal antibody. COVID-19 vaccine recommendations for pregnancy diverged between CDC and ACOG in 2025; confirm in the current guideline.

Rh immune globulin timing

If Rh immune globulin was missed within 72 hours, it should still be given, because some protection exists up to 28 days.

Third trimester and 36 weeks

GBS rectovaginal culture is collected at 36 0/7 to 37 6/7 weeks, which gives a result valid for a 5-week window that covers most term births. Patients with GBS bacteriuria in the current pregnancy or a previous infant with GBS disease skip the culture and receive intrapartum prophylaxis. Intravenous penicillin is the drug of choice during labor; for penicillin allergy, low-risk histories receive cefazolin, while high-risk allergies use clindamycin if the isolate is susceptible, otherwise vancomycin. Antibiotics before labor do not prevent early-onset disease and are not given for a positive culture.

From 36 weeks, check fetal presentation (breech can be offered external cephalic version) and review labor signs, rupture of membranes, decreased fetal movement and bleeding.

Referral and urgent evaluation triggers

• Blood pressure 140/90 or higher on two occasions at least 4 hours apart after 20 weeks, or a severe-range reading of 160/110 or higher, or headache, visual changes, right upper quadrant pain or shortness of breath: evaluate for preeclampsia the same day.
• Vaginal bleeding in the second or third trimester: no digital cervical examination until placenta previa is excluded by ultrasound.
• Decreased fetal movement, leakage of fluid, regular contractions before 37 weeks.
• Positive anti-D or other clinically significant antibody, fundal height lagging by more than 3 cm, or abnormal anatomy ultrasound: maternal-fetal medicine consultation.

Patient education

Avoid alcohol, tobacco and cannabis; limit caffeine to 200 mg a day; avoid undercooked meat, unpasteurized dairy and high-mercury fish; wear seat belts below the abdomen; continue moderate exercise (about 150 minutes a week) unless restricted; report warning signs listed above. Explain why each lab is drawn and when, and plan postpartum contraception and diabetes follow-up before delivery.

How the exam tests this

• Wrong-window distractors: GBS culture at 32 weeks, glucose challenge at 16 weeks in a low-risk patient, or Rh immune globulin at 20 weeks without a sensitizing event.
• Sensitized versus unsensitized: Rh immune globulin is wrong when the antibody screen already shows anti-D.
• Live vaccines: MMR or varicella during pregnancy is wrong; give them postpartum.
• Glucose cut-offs: the 1-hour challenge is a screen, not a diagnosis; a value of 145 leads to a 3-hour test, not to insulin.
• Bacteriuria: asymptomatic bacteriuria in pregnancy is treated, unlike in nonpregnant adults.
• GBS bacteriuria: a patient with GBS in the urine earlier in pregnancy needs no 36-week culture.
• Syphilis: rescreening in the third trimester is now universal under ACOG's 2024 advisory, not risk-based.

Practice question

A 27-year-old G2P1 at 28 weeks' gestation returns for a routine visit. Her blood type is O negative with a negative antibody screen at the first visit. Her first pregnancy was uncomplicated. Today her 1-hour 50 g glucose challenge result is 152 mg/dL, and her blood pressure is 118/72 mm Hg. Which plan is most appropriate?

• A. Diagnose gestational diabetes, start insulin, and give Rh immune globulin at delivery only if the infant is Rh positive.
• B. Order a 3-hour 100 g glucose tolerance test, repeat the antibody screen and give Rh immune globulin 300 mcg today if it remains negative.
• C. Repeat the 1-hour glucose challenge in 2 weeks and give Rh immune globulin at 36 weeks with the GBS culture.
• D. Order a 3-hour glucose tolerance test and hold Rh immune globulin until the partner's blood type is known.

Answer: B. A positive 1-hour challenge is a screening result that requires a diagnostic 3-hour test, and an Rh-negative unsensitized patient receives Rh immune globulin at 28 weeks after a repeat antibody screen. Option A skips the diagnostic test and omits the antenatal dose, giving prophylaxis only at delivery. Option C repeats a screen that is already positive and moves Rh immune globulin to the wrong week. Option D is wrong because routine antenatal prophylaxis is not withheld while waiting for paternal typing, since paternity and partner type are not always certain.

Key points

Related NPPace guides

• Well-Child Visits for the FNP Exam: Milestones by Age, Screening Schedule and Immunizations
• Acute Otitis Media: Diagnosis Criteria, Watchful Waiting vs Antibiotics and the Dosing the Exam Expects
• Contraception by Medical Condition: Using the US MEC on the FNP Exam
• How to Read a Primary-Care Vignette Like a Provider: The 5-Step Method
• AANP vs ANCC: Which NP Certification Exam Should You Take?