Antepartum care (second trimester): Clinical sciences

Second trimester antepartum care refers to pregnancy care from 14 weeks of gestation through 27 weeks and 6 days of gestation. It is critical that patients receive appropriate care during this time of rapid fetal growth and development to prevent complications and optimize pregnancy outcomes.

During this time, all patients in the second trimester warrant an obstetrical ultrasound; genetic counseling; screening for abdominal wall and open neural tube defects; gestational diabetes screening; consideration of repeat antibody screening; and trimester-specific pregnancy education.

When assessing a patient presenting for a second trimester antepartum visit, your first step is to obtain a focused history and physical. The history may reveal common symptoms, such as nausea, vomiting, heartburn, and round ligament pain. Patients may report feeling fetal movement once around 20 weeks, but it may be as early as 16 weeks; this is called quickening. It’s also important to review aspects of the first trimester history, like rescreening for depression, anxiety, and intimate partner violence at least once per trimester.

Your focused physical should include reviewing weight, as both insufficient and excess weight gain can result in complications. Trend blood pressure as well, as two or more elevations prior to 20 weeks suggest chronic hypertension, and after 20 weeks it could indicate gestational hypertension. Perform fetal heart rate Doppler assessment at each visit. Starting at 20 weeks of gestation, include a fundal height to track uterine growth, as well to screen for macrosomia and growth restriction.

With the history and physical complete, it’s time to initiate second trimester antepartum care. Perform an obstetric ultrasound between 18 and 22 weeks of gestation. During this ultrasound, assess the cervical length, placental location, and fetal anatomy. A short cervical length of less than 25 mm may indicate an increased risk of preterm birth. Vaginal progesterone could be considered as a treatment option for patients with a shortened cervix who also have a history of preterm birth and singleton gestation. Also, examine placental location in the uterus, such as anterior or posterior, and to evaluate for placenta previa or vasa previa. A complete survey of fetal anatomy allows for counseling and delivery at an appropriate facility if there is an anomaly.

Some patients may have had their due date established or confirmed by a first trimester ultrasound; however, if no prior ultrasound has been performed, the second trimester ultrasound can be used to confirm dates. Now, if there is evidence of early onset growth restriction at the time of the fetal anatomic survey, a follow up growth ultrasound should be obtained about 4 weeks later. Additionally, if there is a high risk of a fetal cardiac defect, like in patients with pregestational diabetes, or in those with a prior child affected by a cardiac defect, refer for a fetal echocardiogram. This will give you more detailed views of the heart than the standard fetal anatomic survey. Also, if all views cannot be seen on the anatomy ultrasound or abnormalities are noted, repeat imaging may be done later in the second trimester as a follow up.

Here's a clinical pearl! In the second trimester, the due date is determined 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 between 14 weeks and 15 weeks 6 days, assign a new due date if the gestational age by ultrasound is more than 7 days off from menstrual dates. Between 16 weeks and 21 weeks and 6 days, redate the pregnancy if measurements are more than 10 days different. If the patient is between 22 weeks and 27 weeks and 6 days, adjust the due date if measurements are more than 14 days apart.

Remember, the earliest ultrasound is the most accurate to determine the due date! So, if a prior ultrasound has been performed, use that first ultrasound to establish the due date, and don’t redate based on a later ultrasound.

Next up is genetic counseling for all patients. This means presenting options for both screening and diagnostic testing. Many patients had this testing done in the first trimester, and if so, there is no need to repeat it. But if not, cover this in the second trimester. For diagnostic testing, amniocentesis is performed any time after 15 weeks of gestation. Amniocentesis, like chorionic villus sampling in the first trimester, looks not only for fetal aneuploidies but also disorders of single genes, such as DiGeorge syndrome or achondroplasia. There are also noninvasive screening tests that focus on aneuploidies.