A 32-year-old woman, gravida 2 para 0 aborta 1, at 29 weeks gestation comes to the office for a prenatal visit. She has had no vaginal bleeding or contractions. Fetal movement is normal. The pregnancy is dated by an 8-week ultrasound because the patient was unsure of her last menstrual period. Ultrasound at that time showed a 2-cm, pedunculated fibroid at the fundus but was otherwise normal. Repeat ultrasound at 20 weeks gestation showed no fetal abnormalities; the fibroid again measured 2 cm. The patient has no chronic medical conditions. Laboratory results at 28 weeks gestation are as follows: Vital signs at today's visit are normal. Fundal height is 35 cm. Fetal heart tones are 155/min. Which of the following is the most likely underlying cause of this patient's uterine size-dates discrepancy?

Question

A 32-year-old woman, gravida 2 para 0 aborta 1, at 29 weeks gestation comes to the office for a prenatal visit.  She has had no vaginal bleeding or contractions.  Fetal movement is normal.  The pregnancy is dated by an 8-week ultrasound because the patient was unsure of her last menstrual period.  Ultrasound at that time showed a 2-cm, pedunculated fibroid at the fundus but was otherwise normal.  Repeat ultrasound at 20 weeks gestation showed no fetal abnormalities; the fibroid again measured 2 cm.  The patient has no chronic medical conditions.  Laboratory results at 28 weeks gestation are as follows:  Vital signs at today's visit are normal.  Fundal height is 35 cm.  Fetal heart tones are 155/min.  Which of the following is the most likely underlying cause of this patient's uterine size-dates discrepancy?

Quizplus · Accepted Answer

Explanation: 11ec25c8_da5a_7197_bc81_8f7c98c21e80_MD0003_00 This patient at 29 weeks gestation whose fundal height is 35 cm has a uterine size-dates discrepancy. Fundal height (ie, uterine size) is measured during routine prenatal visits in the second and third trimesters as an indirect assessment of fetal growth and amniotic fluid volume. After 20 weeks gestation, fundal height in centimeters should directly correlate to gestational age in weeks with a small variation (eg, ±2-3 cm); therefore, this patient's 6-cm uterine size-dates discrepancy (35 − 29 = 6 cm) is abnormal (Choice C). In this patient, who has a 1-hour glucose tolerance test (GTT) of ≥200 mg/dL, the most likely cause of a uterine size-dates discrepancy is gestational diabetes mellitus (GDM). A presumptive diagnosis of GDM can be made with a very elevated 50-g 1-hour GTT (eg, ≥200 mg/dL) or confirmed with a 100-g 3-hour GTT. 3-hour GTT GDM causes a uterine size-greater-than-dates discrepancy by the following mechanisms: Excess maternal blood glucose crosses the placenta, causing fetal hyperglycemia and increased production of insulin and insulin-like growth factor. This promotes fetal growth and fat deposition, resulting in fetal macrosomia. Fetal hyperglycemia induces osmotic diuresis and polyuria, which increase amniotic fluid volume, resulting in polyhydramnios. A uterine size-dates discrepancy requires further evaluation with ultrasound to measure fetal growth and amniotic fluid volume. (Choice B) Incorrect pregnancy dating is a common cause of uterine size-dates discrepancies. However, this patient's pregnancy is dated by an early first-trimester ultrasound, which is the most precise method (ie, within 5-7 days) for establishing gestational age. (Choice D) Rh alloimmunization can cause hydrops fetalis with associated polyhydramnios and subsequent uterine enlargement. Although this patient is Rh negative and therefore at risk for Rh alloimmunization, her anti-D antibody screening is negative, making this diagnosis unlikely. hydrops fetalis (Choice E) A large uterine leiomyoma (ie, fibroid) may increase fundal height measurement; however, a small (eg, 2-cm) fibroid is unlikely to account for such a large uterine size-dates discrepancy. Although fibroids can change size during pregnancy, they typically grow in the first trimester, and the majority (>50%) remain stable in size. fibroid Educational objective: A uterine size-dates discrepancy exists when the fundal height measures larger or smaller than expected for gestational age. Gestational diabetes mellitus causes a uterine size-greater-than-dates discrepancy by promoting fetal macrosomia and/or increased amniotic fluid volumes (ie, polyhydramnios). References: Etiology and perinatal outcome of polyhydramnios. (http://www.ncbi.nlm.nih.gov/pubmed/24729436) Polyhydramnios: causes, diagnosis and therapy. (http://www.ncbi.nlm.nih.gov/pubmed/24771905)

A 32-Year-Old Woman, Gravida 2 Para 0 Aborta 1, at 29