Pregnancy Risk Factors and Pregnancy Dating

A 38yo primigravida presents for second-trimester ultrasonography. At her first prenatal visit, she reported a sure last menstrual period that was consistent with 6 weeks of gestation. Ultrasonography at that time demonstrated a mean sac diameter consistent with 5 0/7 weeks of gestation. Two weeks later, ultrasonography demonstrated an intrauterine pregnancy with a crown-rump length consistent with a gestational age of 18 0/7 weeks of gestation. The parameter that most accurately establishes this patient’s due date is her

Last menstrual period

Ultrasonography at 5 weeks of gestation

Ultrasonography at 7 weeks of gestation

Ultrasonography at 18 weeks of gestation

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· The traditional method of assigning a due date based on the first day of LMP assumes a 28-day cycle with ovulation on day 14. Given the variation in the cycle and the improved precision of early ultrasound, ultrasound has become an important tool to establish accurate pregnancy dating.

· The earliest ultrasound biometric measurements are the most accurate given that as pregnancy progresses normal fetal growth is associated with greater variation in biometric parameters. There remains a margin of error of 5-7 days in the first trimester. The margin of error is increased in the second and third trimesters.

· Mean gestational sac diameter is less accurate for the establishment of gestational age than measurement of the crown-rump length, and therefore it is not recommended to use the gestational sac measurement to establish gestational age. After 14 0/7, measurements of the biparietal diameter, head circumference, abdominal circumference and femur length should be used to calculate gestational age.

· If pregnancy is the result of artificial reproductive technology and the date of embryo transfer or insemination is known, these data should be used to establish the due date. For multiple gestations with discrepancies in sizes, gestational age is generally assigned to correspond to the ultrasonographic size of the larger fetus.

A 26yo woman, G3P2, presents to your office at 12 weeks of gestation. Her BMI is 40. Her surgical medical, and family histories are noncontributory. You discuss that her obesity places her at increased risk of congenital anomalies compared with a nonobese woman. The structural malformation with the highest attributable increased risk in this patient is

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· Obesity affects 32% of reproductive-aged women. Obese women are at an increased risk of fetal and maternal complications, and risks increase as the BMI category increases.

· The highest attributable increased risk from obesity is neural tube defects, although there is also an increased risk of cardiac anomalies, orofacial clefting, limb reduction anomalies, and anorectal atresia.

· Maternal complications related to obesity include obstructive sleep apnea, gestational diabetes, preeclampsia, and cardiac dysfunction. During the intrapartum period, patients are at an increased risk of failed induction, cesarean delivery, wound morbidity, and venous thromboembolism. With each five-unit increase in BMI after 25, there is an approximately 1.2-fold increased risk of perinatal, neonatal, and infant mortality.

Discuss early screening for diabetes in pregnancy. Who should be screened, and how?

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· It is estimated at approximately 30 percent of females age 18-44 years in the US have diagnosed or undiagnosed impaired glucose metabolism. Testing for diabetes during early pregnancy can identify people with undiagnosed type 2 diabetes and allow for earlier initiation of treatment to improve pregnancy outcomes.

· ACOG recommends consideration for early testing for women at the initial prenatal visit for women who have a BMI >25 and one or more of these additional risk factors: physical inactivity, first degree relative with diabetes, high-risk race or ethnicity (Black, Latinx, Native American, Asian American, Pacific Islander), prior infant weighing at least 4000g, previous gestational DM, HTN, abnormal cholesterol screening, PCOS, A1c of 5.7% or greater, or history of cardiovascular disease.

· Early testing can be accomplished with a screening 1-hour 50g oral glucose tolerance test (OGTT), followed by a diagnostic 3-hour 100g OGTT. If the screening is negative, then it is recommended to repeat it at 24-28 weeks. For those with an elevated early 1-hour OGTT but normal diagnostic testing, it is typical to repeat only the 3-hour OGTT at 24-28 weeks. Using a hemoglobin A1c alone for early screening has decreased sensitivity compared to an OGTT as the A1c is decreased by hemodilution and increased red blood cell turnover during pregnancy.