Magnusson A, et al. - Researchers investigated the association between the number of oocytes retrieved for in vitro fertilization (IVF) and perinatal and obstetric outcomes via performing a retrospective population-based registry study including all singleton babies born after fresh IVF cycles from 2002 to 2015 (n=27,359) in Sweden. Findings revealed no significant association between the number of oocytes retrieved and perinatal outcomes, while there appeared to be an association of placenta previa with male sex.

Methods

• For maternal and neonatal outcome, researchers cross-linked data from the Medical Birth/IVF Registry and the Swedish National Quality Registry of Assisted Reproduction on treatment characteristics, including all fresh IVF cycles performed in public or private infertility clinics during the study period and resulting in singleton deliveries, to the Medical Birth Registry and the National Patient Registry.
• They obtained data on educational level, ethnicity, and paternal age via cross-linking to Statistics Sweden.
• They excluded oocyte donation cycles.
• Preterm birth (PTB < 37 gestational weeks), very PTB (< 32 gestational weeks), small for gestational age (SGA: < 2 SD), peri/neonatal death, and major birth defects were the main perinatal outcome variables assessed.
• Hypertensive disorders of pregnancy and placenta previa were the main obstetric outcome variables assessed.
• Univariable and multivariable analyses were used to explore the association between the number of oocytes retrieved and outcome variables.
• They performed adjustments for maternal age, parity, smoking, body mass index, cause of infertility, maternal educational level, maternal country of birth, treatment period, embryo stage, fertilization method (IVF/ICSI), number of embryos transferred, ovarian hyperstimulation syndrome, and vanishing twin.

Results

• Researchers analyzed the number of oocytes retrieved as a continuous variable and categorized the number as <10, 10–14, 15–19, and >20 oocytes.
• As a reference, they used a number of between four and nine oocytes.
• In 20,910 (76.4%) of the cycles, single embryo transfer was performed.
• In 3,478 (12.7%) of the cycles, blastocyst transfer was performed, and in 23,881 (87.3%), cleavage stage embryo transfer was performed.
• They identified that the number of oocytes retrieved (continuous variable) was not significantly correlated with PTB, very PTB, SGA, peri/neonatal death, or major birth defects.
• Concerning obstetric outcomes, they noted a significant association for placenta previa (AOR: 1.021, 95% CI: 1.005–1.037) while no association for hypertensive disorders of pregnancy (AOR: 0.991, 95% CI: 0.981–1.001).
• Furthermore, the number of oocytes retrieved was significantly associated with the secondary outcome variable sex distribution, with a higher rate of males after > 20 oocytes (AOR: 1.126, 95% CI: 1.014–1.249).