Obstetrics and Gynecology Flashcards

A 34-year-old woman at 28 weeks gestation presents with sudden-onset severe headache, visual disturbances, and a blood pressure of 162/110 mmHg. Urinalysis shows 3+ proteinuria. She is started on magnesium sulfate and labetalol. Four hours later, her urine output drops to 18 mL/hour and her serum magnesium level is 9.2 mEq/L. She becomes areflexic. What is the most appropriate next step?

Answer: Administer calcium gluconate 1 g IV and hold further magnesium doses

A serum magnesium level of 9.2 mEq/L with areflexia indicates magnesium toxicity (therapeutic range 4–7 mEq/L; areflexia occurs at ~7–10 mEq/L; respiratory arrest at >12 mEq/L). The antidote is calcium gluconate 1 g IV, which antagonizes magnesium at the neuromuscular junction. Magnesium infusion must be stopped, not merely reduced. Increasing fluids does not address the toxicity, and emergent delivery is not indicated solely by magnesium toxicity without fetal or maternal decompensation.

A 29-year-old G2P1 at 22 weeks gestation undergoes amniocentesis for elevated AFP on quad screen. The amniotic fluid AFP is markedly elevated and acetylcholinesterase is present. Fetal ultrasound reveals a normal-appearing fetus with no visible neural tube defect. What is the most likely explanation?

Answer: Fetal sacrococcygeal teratoma

The combination of elevated amniotic fluid AFP AND positive acetylcholinesterase (AChE) confirms fetal origin rather than contamination. AChE is present in fetal neural tissue and exposed skin/gut. When the neural tube appears intact on ultrasound, other open fetal defects must be considered — sacrococcygeal teratoma is a classic cause of elevated AFP with positive AChE and no visible NTD. Blood contamination would not produce AChE. Placental mesenchymal dysplasia can elevate AFP but does not produce AChE. Confined placental mosaicism does not elevate AChE.

A 41-year-old woman undergoes a hysteroscopic myomectomy for a 4 cm submucosal fibroid. The procedure takes 90 minutes with 6 liters of 1.5% glycine distension medium used and 5.2 liters recovered. Postoperatively she develops nausea, headache, and confusion. Serum sodium returns at 118 mEq/L. What is the most serious potential complication directly attributable to the glycine specifically (as opposed to another hypotonic medium)?

Answer: Hyperammonemia from glycine metabolism

While hyponatremia (answer B) can occur with any hypotonic medium, glycine is specifically metabolized to ammonia via glycine decarboxylase, which can cause hyperammonemic encephalopathy independent of the sodium level. This is unique to glycine-containing media and can be fatal if unrecognized. Transient visual disturbances (scotomata) can also occur with glycine due to its inhibitory neurotransmitter properties, but hyperammonemia represents the most serious and glycine-specific risk. Hemolysis is more characteristic of sterile water as distension medium. The question specifically asks what is attributable to glycine itself.

A 52-year-old postmenopausal woman presents with a 3 cm unilateral adnexal mass. CA-125 is 28 U/mL (normal). Transvaginal ultrasound shows a unilocular, thin-walled cyst with no internal septations, papillations, or solid components. She has no family history of ovarian or breast cancer. What is the most evidence-based management?

Answer: Annual ultrasound surveillance without intervention

According to ACOG/SGO guidelines, simple unilocular adnexal cysts ≤10 cm in postmenopausal women with normal CA-125 have a very low malignancy risk (<1%). Annual surveillance ultrasound is the appropriate management — surgical excision is not routinely required. This represents a shift from older teaching that all postmenopausal adnexal masses required surgery. Repeat ultrasound in 6 weeks is too soon without a specific clinical reason. MRI adds cost without changing management for morphologically simple cysts. The absence of complex features (septations, papillations, solid areas) is the key discriminator.

A 26-year-old woman with known antiphospholipid syndrome (APS) confirmed by two positive lupus anticoagulant tests 12 weeks apart presents at 8 weeks gestation. She has a history of one prior pregnancy loss at 18 weeks (morphologically normal fetus). She is currently on hydroxychloroquine. What is the most appropriate antithrombotic regimen during this pregnancy?

Answer: Low-dose aspirin plus prophylactic-dose low molecular weight heparin

This patient meets criteria for obstetric APS (confirmed APS plus one fetal loss ≥10 weeks with morphologically normal fetus). The standard of care is combination low-dose aspirin (81 mg/day) PLUS prophylactic-dose LMWH (e.g., enoxaparin 40 mg SQ daily). Aspirin alone is insufficient for this level of risk. Therapeutic LMWH alone omits the antiplatelet effect of aspirin. Corticosteroids (prednisone) are not first-line and add risks of gestational diabetes, preeclampsia, and premature rupture of membranes without proven benefit over combination aspirin/heparin. Hydroxychloroquine is maintained as it may have additional antithrombotic benefits.

A 38-year-old G3P2 at 36 weeks gestation with dichorionic-diamniotic twins presents for a routine visit. Twin A is vertex, Twin B is transverse. She desires vaginal delivery. Estimated fetal weights are Twin A 2,550 g and Twin B 2,480 g. Which factor would most absolutely contraindicate an attempt at vaginal delivery in this case?

Answer: Twin B estimated weight >20% larger than Twin A

When Twin B is significantly larger than Twin A (discordance >20%), vaginal delivery of Twin A first can result in entrapment or obstruction when attempting delivery of the larger Twin B — this is an absolute contraindication to planned vaginal delivery of twins. Twin B's transverse lie is NOT an absolute contraindication because it may be managed with external cephalic version or internal podalic version followed by breech extraction after Twin A delivers and the uterus is still relaxed. Advanced maternal age and late preterm gestational age are not contraindications. The weight discordance threshold of >20% is the key absolute contraindication listed here.