Antepartum care (third trimester): Clinical sciences

Third trimester antepartum care refers to pregnancy care from 28 weeks of gestation through the end of pregnancy. Care during this time is critical to monitor for high-risk conditions and prepare for delivery. All patients in the third trimester warrant consideration of additional ultrasounds; screening tests; assessment of fetal well-being; counseling on birth plans; trimester-specific pregnancy education; and counseling on postpartum contraception.

When assessing a patient presenting for a third trimester antepartum visit, your first step is to obtain a focused history and physical. The history should include asking whether they’re experiencing contractions, possible leakage of fluid, vaginal bleeding, and appropriate fetal movements.

Additionally, patients may report common benign pregnancy symptoms, such as Braxton Hicks contractions, back aches, round ligament pain, edema, acid reflux, and mild shortness of breath

Here's a clinical pearl! Braxton Hicks contractions, often referred to as “false labor,” present with infrequent and minimally painful tightening of the abdomen. On the flip side, contractions representing “true labor” are painful, regular, and increase in frequency over time. Typically, false labor is felt only in the front of the abdomen, while true labor is felt in the lower back as well as the abdomen.

Your physical exam should include a review of weight, since both insufficient and excessive weight gain can lead to complications. Also, pay attention to blood pressure, as new elevations could indicate gestational hypertension or preeclampsia. Perform fetal Doppler assessment at each visit and follow up on any abnormality with prolonged monitoring.

With the focused history and physical complete, it’s time to initiate third trimester antepartum care.

For patients with abnormal fundal heights or those with conditions that raise the risk of macrosomia or growth restriction, growth ultrasounds are done every 3 to 4 weeks. Some patients may have had a prior ultrasound that showed an abnormality, such as placenta previa or a fetal anomaly, so reassess any previous abnormalities in the third trimester. While uncommon, some patients with insufficient prenatal care get to the third trimester without having an ultrasound and require assessment of their due date.

Here's a clinical pearl! In the third trimester, the due date is assessed by comparing the gestational age calculated by the last menstrual period to fetal biometry, meaning an assessment of the fetal head, abdomen, and extremities. For pregnancies at 28 weeks and beyond that have not previously had ultrasound confirmation of their due date, assign a new due date if the gestational age by ultrasound is more than 21 days off from menstrual dates.

Keep in mind that in cases where there is no ultrasound confirmation of dates before 22 weeks of gestation, the pregnancy would be considered suboptimally dated. This means that timing for indicated deliveries, such as those with preeclampsia, should be based on the best clinical estimates. Also, suboptimally dated pregnancies are not candidates for elective delivery after 39 weeks and 0/7 days.

Next up, let’s talk about different screening assessments in the third trimester. If not already done in the second trimester, be sure to order a CBC around 28 weeks to reassess for anemia, as well as a glucose tolerance test to screen for gestational diabetes. Patients at high-risk for infectious diseases need repeat screening for HIV, syphilis, gonorrhea, and chlamydia. Unless a patient is already known to be a carrier of group B streptococcus, collect a vaginal-rectal swab between 36 and 38 weeks.

Additionally, assess fetal presentation at approximately 36 weeks by palpating through the Leopold maneuvers, or by a limited ultrasound exam if the patient’s body habitus prevents adequate assessment. If the fetus has a breech presentation or transverse lie at or after 36 weeks, counsel on the external cephalic version, or ECV. Finally, repeat depression and intimate partner violence screening as well, usually at the 28-week visit.

Here’s another clinical pearl! ECV is a procedure performed after 37 weeks, where providers will attempt to move the fetus into a cephalic presentation by applying external pressure on the patient's abdomen. ECV is elective, meaning that after you explain the risks and benefits, your patient can choose to have it performed in order to prevent a c-section. If ECV fails, or if the patient declines, the next step for delivery would be a c-section