Abstract
Study question
We aimed to compare obstetric and perinatal outcomes between pregnancies conceived by in vitro fertilization (IVF) with fresh embryo transfer and frozen embryo transfer (FET) in the same women.
Summary answer
IVF pregnancies following fresh and FET entailed the same obstetric and perinatal outcomes, when compared in the same women. What is known already: There seems to be a difference in adverse outcomes between pregnancies following fresh and FET, as fresh transfer has repeatedly been associated with a higher risk of preterm birth and small for gestational age neonates, and the FET with preeclampsia and large for gestational age neonates. The overall lower incidence of adverse obstetric outcomes in FET may relate to the transfer of an embryo to a uterine environment in the setting of more physiological estradiol level but may also relate to patient characteristics which allow for freezing and subsequent transfer.
Study design, size, duration
This was a retrospective cohort of 214 deliveries during a 13-year period.
Participants/materials, setting, methods
The study was performed in a tertiary hospital. The cohort included live singleton deliveries (>24 weeks of gestation) and excluded pregnancies following egg donation. Each fresh transfer IVF pregnancy was matched to a FET pregnancy by the same woman (1:1 ratio).
Main results and the role of chance
A total of 107 fresh transfer pregnancies were matched to 107 FET pregnancies, in the same women. Mean maternal age was lower in the fresh transfer group compared to the FET group (30.4 vs. 32.5 years, p < 0.001), as was body mass index (BMI) (p = 0.001). A higher rate of nulliparity was noted in fresh transfer pregnancies (64.5% vs. 12.1%, p < 0.001). Mean birthweight was higher in the FET group (3160 vs. 3081 grams, respectively, p < 0.001), although the rates of low birth weight and small for gestational age neonates did not differ between the groups. Preterm deliveries occurred in 10.3% and 9.3% of fresh transfer and FET pregnancies respectively, p = 0.79. On multivariate linear regression analysis, the type of embryo transfer - FET or fresh - was not independently associated with birthweight, after adjustment for women’s age, nulliparity and BMI.
Limitations, reasons for caution
The study relied on coding in patient files, and thus certain data were missing for analysis, such as paternal identity. In addition, women included had at least two successful IVF pregnancies, and at least one cycle in which embryo freezing was performed. This may confer a selection bias.
Wider implications of the findings: Our study of sibling deliveries after fresh and FET, points to a similar prognosis for the main obstetric and perinatal outcomes. This adds to current research which points to similar development of children following fresh and FET and is reassuring for clinicians consulting patients who are eligible for both options.
Trial registration number
Not applicable
First trimester vaginal bleeding does not predict small for gestational age newborns following single euploid frozen embryo transfer
