Box 2.

General principles for routine ultrasounds to maximize perinatal diagnosis and minimize exposure risk

Dating ultrasound: •Combine dating/NT to one ultrasound based on LMP. •If ultrasound earlier in the first trimester (eg, less than 10 weeks) is indicated because of threatened abortion, pregnancy of unknown anatomic location, may consider forgoing NT ultrasound and offering cell-free DNA screening for those desiring early aneuploidy screening. •For patients with unknown LMP or EGA >14 weeks may schedule as next available. Anatomy ultrasound (20–22 weeks)a •Consider follow-up views in 4–8 weeks rather than 1–2 weeks.b •Consider serial cervical length for those at highest risk for spontaneous preterm birth, otherwise do once with anatomy ultrasound. •BMI >40 kg/m2: schedule at 22 weeks to reduce risk of suboptimal views/need for follow-up. Growth ultrasounds •All single third-trimester growth at 32 weeks. •Follow-up previa/low-lying placenta at 34–36 weeks. •Begin serial growth at 28 weeks (not 24 weeks) with rare exceptions. •Consider q 6–8 weeks week rather than q 4 week follow-up for most patients,

NT, nuchal translucency; LMP, last menstrual period; EGA, estimated gestational age; BMI, body mass index; q, every.

^aOr earlier if desired based on state-specific termination laws.

^bConsider forgoing follow-up ultrasound for 1 or 2 suboptimal views (eg, l/s spine not seen well because of fetal position but posterior fossa normal).

Boelig. MFM guidance for COVID-19. Am J Obstet Gynecol MFM 2020.