A 24-year-old primigravida presents to her physician for regular prenatal care at 31 weeks gestation. She has no complaints and the antepartum course has been uncomplicated. Her pre-gestational history is significant for obesity (BMI = 30.5 kg/m2). She has gained a total of 10 kg (22.4 lb) during pregnancy, and 2 kg (4.48 lb) since her last visit 4 weeks ago. Her vital signs are as follows: blood pressure, 145/90 mm Hg; heart rate, 87/min; respiratory rate, 14/min; and temperature, 36.7℃ (98℉). The fetal heart rate is 153/min. The physical examination shows no edema and is only significant for a 2/6 systolic murmur best heard at the apex of the heart. A 24-hour urine is negative for protein. Which of the following options describe the best management strategy in this case?

Observation in the outpatient settings

Treatment in outpatient settings with labetalol

Treatment in the outpatient settings with nifedipine

Treatment in the inpatient settings with methyldopa

Admission to hospital for observation

A 29-year-old G1P0 presents to her obstetrician for her first prenatal care visit at 12 weeks gestation by last menstrual period. She states that her breasts are very tender and swollen, and her exercise endurance has declined. She otherwise feels well. She is concerned about preterm birth, as she heard that certain cervical procedures increase the risk. The patient has a gynecologic history of loop electrosurgical excision procedure (LEEP) for cervical dysplasia several years ago and has had negative Pap smears since then. She also has mild intermittent asthma that is well controlled with occasional use of her albuterol inhaler. At this visit, this patient’s temperature is 98.6°F (37.0°C), pulse is 69/min, blood pressure is 119/61 mmHg, and respirations are 13/min. Cardiopulmonary exam is unremarkable, and the uterine fundus is just palpable at the pelvic brim. Pelvic exam reveals normal female external genitalia, a closed and slightly soft cervix, a 12-week-size uterus, and no adnexal masses. Which of the following is the best method for evaluating for possible cervical incompetence in this patient?

Transvaginal ultrasound at 18 weeks gestation

Transabdominal ultrasound in the first trimester

Transvaginal ultrasound in the first trimester

Serial transvaginal ultrasounds starting at 16 weeks gestation

Transabdominal ultrasound at 18 weeks gestation

A 26-year-old woman presents to the women’s health clinic with a 9-week delay in menses. The patient has a history of grand mal seizures, and was recently diagnosed with acute sinusitis. She is prescribed lamotrigine and amoxicillin. The patient smokes one-half pack of cigarettes every day for 10 years, and drinks socially a few weekends every month. Her mother died of breast cancer when she was 61 years old. The vital signs are stable during the current office visit. Physical examination is grossly normal. The physician orders a urine beta-hCG that comes back positive. Abdominal ultrasound shows an embryo consistent in dates with the first day of last menstrual period. Given the history of the patient, which of the following would most likely decrease congenital malformations in the newborn?

Switching to another antiepileptic medication

Weight gain recommendations for USMLE Step 3: High-Yield OB/GYN Lessons

BMI Categories - The Starting Line

Pre-pregnancy Body Mass Index (BMI) is the foundational metric for determining appropriate gestational weight gain. It's calculated before or at the first prenatal visit.

Formula: $BMI = weight (kg) / [height (m)]^2$

Category	BMI (kg/m²)
Underweight	< 18.5
Normal weight	18.5-24.9
Overweight	25.0-29.9
Obese	≥ 30.0

⭐ Pre-pregnancy BMI is one of the strongest predictors of adverse maternal and fetal outcomes, including gestational diabetes, hypertension, and macrosomia.

IOM Guidelines - The Growing Game

Optimal maternal weight gain is tailored to the pre-pregnancy Body Mass Index (BMI) to ensure fetal well-being and minimize maternal complications. The Institute of Medicine (IOM) provides the standard recommendations used in the US.

Pre-pregnancy BMI (kg/m²)	BMI Category	Recommended Total Gain	Rate (2nd/3rd Tri)
< 18.5	Underweight	28-40 lbs (12.5-18 kg)	~1 lb/week
18.5-24.9	Normal weight	25-35 lbs (11.5-16 kg)	~1 lb/week
25.0-29.9	Overweight	15-25 lbs (7-11.5 kg)	~0.6 lb/week
≥ 30.0	Obese	11-20 lbs (5-9 kg)	~0.5 lb/week

⭐ For patients with obesity, even weight gain below the IOM guidelines may be associated with favorable outcomes, such as a lower risk of large-for-gestational-age (LGA) infants and cesarean delivery, without increasing the risk of small-for-gestational-age (SGA) infants.

Risks & Management - The Balancing Act

Maternal Diet Impact on Fetal Development and Child Health

Risks of Excessive Gain
- Maternal: ↑ Gestational Diabetes (GDM), hypertensive disorders, Cesarean delivery, postpartum weight retention.
- Fetal: Macrosomia (>4.0-4.5 kg), shoulder dystocia, birth trauma, neonatal hypoglycemia, childhood obesity.
Risks of Inadequate Gain
- Fetal: Fetal Growth Restriction (FGR), Small for Gestational Age (SGA), preterm birth.
Management
- Diet: Counseling on balanced nutrition; dietitian referral if needed.
- Exercise: ≥150 minutes/week of moderate-intensity activity (e.g., walking, swimming), if not contraindicated.
- Monitoring: Regular weight checks to track gain velocity.

⭐ Excessive gestational weight gain is a strong independent predictor for Cesarean delivery, regardless of fetal macrosomia.

High‑Yield Points - ⚡ Biggest Takeaways

IOM guidelines stratify weight gain recommendations by pre-pregnancy BMI.

Underweight (<18.5 BMI): Gain 28-40 lbs.

Normal weight (18.5-24.9 BMI): Gain 25-35 lbs. This is the most tested range.

Overweight (25-29.9 BMI): Gain 15-25 lbs.

Obese (≥30 BMI): Gain 11-20 lbs.

Inadequate gain is linked to fetal growth restriction, while excessive gain increases risks for macrosomia and cesarean delivery.

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