Prenatal Care: Labs, Fundal Height and Danger Signs

Maternal & Newborn · Antepartum / Prenatal Care·Updated 2026-10-28

What it is

Prenatal care finds conditions that harm the client or fetus early enough to treat them. Pregnancy changes physiology: plasma volume rises more than red cell mass (physiologic anemia), heart rate rises 10 to 15/min, and the enlarging uterus compresses the vena cava when the client lies supine. Most prenatal questions ask the nurse to separate these expected changes from danger signs.

What the NCLEX focuses on

Naegele rule: first day of the last menstrual period minus 3 months plus 7 days.
From 20 to 36 weeks, fundal height in centimeters equals weeks of gestation; a difference of more than 2 cm needs evaluation, usually a growth ultrasound.
First-visit labs: CBC, blood type, Rh and antibody screen, rubella and varicella immunity, hepatitis B surface antigen, hepatitis C, HIV, syphilis, urine culture, and chlamydia and gonorrhea screening.
At 24 to 28 weeks: 1-hour glucose challenge test, repeat hemoglobin, and antibody screen with Rh immune globulin 300 mcg at 28 weeks for the Rh-negative client.
Group B Streptococcus rectovaginal culture at 36 0/7 to 37 6/7 weeks; a positive result means IV penicillin in labor.
Rh immune globulin is also given within 72 hours of birth of an Rh-positive newborn and after bleeding, amniocentesis, pregnancy loss or abdominal trauma.
Inactivated influenza vaccine is given in any trimester and Tdap at 27 to 36 weeks of every pregnancy; MMR and varicella wait until after birth.

Priority nursing actions

At every visit, measure blood pressure, weight and urine protein, and ask about danger signs.
After 10 to 12 weeks, check the fetal heart rate by Doppler; after 20 weeks, measure fundal height.
Turn a client who becomes faint, pale and tachycardic while supine onto her side.
Report blood pressure of 140/90 mm Hg or higher after 20 weeks, especially with headache or visual changes.
Report a fundal height that lags or exceeds dates by more than 2 cm.

Numbers to know

Value	Expected or target	Why it matters
Hemoglobin	11 g/dL (110 g/L) or higher; 10.5 g/dL (105 g/L) in the second trimester	Lower values mean anemia beyond physiologic dilution
Fundal height	Centimeters equal weeks, plus or minus 2 cm (20 to 36 weeks)	Lag suggests growth restriction or low amniotic fluid
Fetal heart rate	110 to 160/min	Outside the range needs evaluation
Glucose challenge (50 g, 1 hour)	Below 140 mg/dL (7.8 mmol/L)	Higher result leads to the 3-hour glucose tolerance test
Weight gain, normal BMI	25 to 35 lb (11.5 to 16 kg)	Too little or too much affects fetal growth
Folic acid	400 mcg daily; 4 mg after a previous neural tube defect	Prevents neural tube defects

Common exam traps

Choosing to document a fundal height 4 cm below dates as normal variation: wrong because a lag of more than 2 cm needs a growth ultrasound.
Choosing to raise the head of the table for supine hypotension: wrong because the uterus still compresses the vena cava; turn the client to her side.
Choosing to give MMR to a nonimmune pregnant client: wrong because MMR is a live vaccine; give it after birth.
Choosing to call a hemoglobin of 10.8 g/dL at 26 weeks iron-deficiency anemia: wrong because it is above the second-trimester threshold and reflects dilution.

What to teach

Report at once: vaginal bleeding, a gush or leak of fluid, fever of 100.4 F (38 C) or higher, vomiting that prevents keeping fluids down, severe headache, visual changes, epigastric pain, sudden swelling of the face or hands, painful urination, regular tightening before 37 weeks, and decreased fetal movement.
From 28 weeks, count fetal movements daily and report fewer than 10 in 2 hours.
Take iron with orange juice between meals, not with milk, calcium or antacids.
Avoid alcohol, unpasteurized cheese and high-mercury fish; limit caffeine to 200 mg a day; have someone else change the cat litter.

Client handout: Pregnancy Warning Signs (nurse guide and printable patient handout).

Try 2 NCLEX-style questions on this topic

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Question 1 · QID 2E5BA36E

At a 30-week visit the nurse measures a fundal height of 26 cm. At the 26-week visit it was 25 cm. The client's dates are confirmed by an early ultrasound and her bladder is empty. Which action should the nurse take?

Select the best answer.

A. Notify the provider so a growth ultrasound can be ordered
B. Repeat the fundal height at the next routine visit in 2 weeks and order additional testing only if the measurement remains behind
C. Increase daily caloric intake by about 500 calories and reassess fundal growth after several weeks of improved maternal nutrition
D. Document the 26-cm fundal height as acceptable variation at 30 weeks because individual maternal body shape can affect measurement

Question 2 · QID 91DF4079

The nurse reviews warning signs with a client at 18 weeks of gestation before she leaves the clinic. Which symptoms should the nurse instruct the client to report immediately? Select all that apply.

A. Chills with a temperature of 38.4 C (101.1 F)
B. A sudden gush of fluid from the vagina
C. Increased whitish vaginal discharge without odor or itching
D. Any vaginal bleeding
E. Vomiting that prevents keeping any fluids down for a day
F. Mild backache after a day of standing

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More tips on Maternal & Newborn

Fetal Heart Rate Patterns and DecelerationsRead baseline, variability and decelerations, match each deceleration to its cause, and give intrauterine resuscitation in the right order.Postpartum Hemorrhage: Recognize Early, Act FastSpot hemorrhage before the blood pressure falls, firm a boggy uterus, empty the bladder, and give uterotonics within their contraindications.Newborn Assessment: Apgar and the First HoursScore the Apgar, know normal newborn vital signs and findings, and give first-hours care: warmth, glucose, vitamin K, eye care and security.

Sources

Perry SE, Hockenberry MJ, Cashion K, Alden KR, Olshansky E, Lowdermilk DL. Maternal Child Nursing Care. 7th ed. Elsevier; 2022.
American College of Obstetricians and Gynecologists. Prevention of Group B Streptococcal Early-Onset Disease in Newborns. ACOG Committee Opinion No. 797. Obstet Gynecol. 2020;135(2):e51-e72.
Institute of Medicine and National Research Council. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: National Academies Press; 2009.

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