The use of frozen-thawed embryo transfer (FET) has increased over the past decade with improvements in technology and increasing live birth rates. FET facilitates elective single-embryo transfer, reduces ovarian hyperstimulation syndrome, optimizes endometrial receptivity, allows time for preimplantation genetics testing, and facilitates fertility preservation. FET cycles have been associated, however, with an increased risk of hypertensive disorders of pregnancy for reasons that are not clear. Recent evidence suggests that absence of the corpus luteum (CL) could be at least partly responsible for this increased risk. In a recent prospective cohort study, programmed FET cycles (no CL) were associated with higher rates of preeclampsia and preeclampsia with severe features compared with modified natural FET cycles. FET cycles are commonly performed in the context of a programmed cycle in which the endometrium is prepared with the use of exogenous E 2 and P. In these cycles, ovulation is suppressed and therefore the CL is absent. The CL produces not only E 2 and P, but also vasoactive products, such as relaxin and vascular endothelial growth factor, which are not replaced in a programmed FET cycle and which are hypothesized to be important for initial placentation. Emerging evidence has also revealed other adverse obstetrical and perinatal outcomes, including postpartum hemorrhage, macrosomia, and post-term birth specifically in programmed FET cycles compared with natural FET cycles. Despite the widespread use of FET, the optimal protocol with respect to live birth rate, maternal health, and perinatal outcomes has yet to be determined. Future practice regarding FET should be based on high-quality evidence, including rigorous controlled trials.

Pregnant women and their fetuses may be impacted disproportionally by emerging infections 1 as exemplified by the 2009 H1N1 influenza pandemic 2 and the severe fetal complications of Zika virus. 3,4 The novel coronavirus infection, severe acute respiratory coronavirus 2 (SARS-CoV-2), was first reported in Wuhan, China, on December 31, 2019, and was declared a pandemic by the WHO on March 11, 2020. 5 Since then, the number of worldwide reported cases of COVID-19 has increased to 6.11 million and 370,000 deaths as of May 31, 2020. 6 To combat the rapidly spreading virus, nations have implemented strategies to suppress and mitigate the community-acquired infections such as social distancing, availability of rapid testing, contact tracing, and vaccine development. 7,8 Coronaviruses are single-stranded RNA, enveloped, non-segmented viruses which cause complications ranging from common cold to pneumonia and death. 9 Common symptoms of SARS-CoV-2 infection include fever, cough, myalgia, headache, and diarrhea. 10 Highly infective, the virus is transmitted to 2-3 people for every infected person, with a reproduction number (R0) of 2.2. 11 While

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