Advantages of delaying embryo transfer after pregnancy loss

Pregnancy outcomes are improved by delaying the next frozen embryo transfer (FET) by at least 6 months after clinical pregnancy loss (CPL), according to a recent study published in JAMA Network Open.

The interpregnancy interval (IPI) refers to the time after the end of a pregnancy until the beginning of a following pregnancy. The length of this period may impact pregnancy outcomes, with data indicating a short IPI after a live birth increases the risks of low birth weight, preterm birth, and small for gestational age.

Women with a CPL usually have a shorter IPI before the next pregnancy than those with a live birth. For women receiving in vitro fertilization (IVF), it is vital to determine when the next cycle of embryo transfer after a CPL should occur. However, debate remains on the appropriate IPI after a CPL.

Investigators conducted a cohort study to determine the association between IPI length after CPL and pregnancy outcomes. Data was obtained from the clinical database of the Center for Reproductive Medicine of Shandong University.

Participants included women receiving a frozen-thawed blastocyst transfer within 1 year following CPL of a prior transfer from July 1, 2017, to June 30, 2022. Live birth after FET was measured as the primary outcome of the analysis, determined by neonate delivery with signs of life at 24 weeks of gestation or later.

Exclusion criteria included history of recurrent pregnancy loss or recurrent implant failure, diagnosis of uterine abnormalities, presenting untreated hydrosalpinx, transferred embryo receiving preimplantation genetic testing, and transferred embryo derived from oocyte donation or oocyte cryopreservation.

There were 2433 women with IVF treatment included in the analysis, aged a mean 31.8 years. Of participants, 13.9% had an IPI under 3 months, 55.4% an IPI of 3 to 6 months, and 30.7% an IPI of 6 to 12 months. These groups had median IPIs of 77 days, 128 days, and 234 days, respectively.

Women with an IPI under 3 months were often older and less often nulliparous than those with an IPI of 3 to 6 months or 6 to 12 months, with a mean 33.7%, 28.2%, and 26.1% respectively aged 35 years or older. Polycystic ovarian syndrome was reported in 13.9% of the IPI under 3 months group, 17.3% of the 3 to under 6 months group, and 21.9% of the 6 to 12 months group.

Having an endometrial thickness under8 mm before FET was also less common in groups with a shorter IPI. The odds of experiencing a preceding CPL in the second trimester in the under 3 months group, the 3 to under 6 months group, and the 6 to 12 months group were 7.4%, 21.4%, and 36.7%, respectively.

Rates of live birth, singleton live birth, and total pregnancy loss were 39.6%, 37.6%, and 39%, respectively in the under 3 months group. In the 3 to under 6 months group, these rates were 42.2%, 40.6%, and 21%, respectively. In the 6 to 12 months group, these rates were 47.2%, 46.3%, and 29.2%, respectively.

The odds of clinical pregnancy, total live birth, singleton live birth, and healthy live birth were all decreased in patients with shorter IPIs. The risks of total biochemical pregnancy loss and total pregnancy loss were also increased in these individuals.

These results indicated improved pregnancy outcomes when delaying FTL by at least 6 months following CPL. Investigators recommended further prospective studies be conducted to confirm these findings.

Reference

Wang Z, Meng Y, Shang X, et al. Interpregnancy interval after clinical pregnancy loss and outcomes of the next frozen embryo transfer. JAMA Netw Open. 2023;6(10):e2340709. doi:10.1001/jamanetworkopen.2023.40709