Multifetal pregnancy reduction (MPR) was developed in the 1980s in the wake of significant increases in the incidence of triplets and other higher-order multiples emanating from assisted reproductive technologies (ART). It was offered to reduce fetal number and improve outcomes for remaining fetuses by reducing rates of preterm delivery, fetal growth restriction, and other adverse perinatal outcomes, as well as maternal complications such as preeclampsia and postpartum hemorrhage.
In recent years, improvements in ART – mainly changes in ovulation induction practices and limitations in the number of embryos implanted to two at most – have reversed the increase in higher-order multiples. However, with intrauterine insemination, higher-order multiples still occur, and even without any reproductive assistance, the reality is that multiple pregnancies – particularly twins – continue to exist. In 2018, twins comprised about 3% of births in the United States.1
Twin pregnancies have a significantly higher risk than singleton gestations of preterm birth, maternal complications, and neonatal morbidity and mortality. The pregnancies are complicated more often by preterm premature rupture of membranes, fetal growth restriction, and hypertensive disorders of pregnancy.
Monochorionic diamniotic twin pregnancies face additional, unique risks of twin-to-twin transfusion syndrome, twin reversed arterial perfusion sequence, and twin-anemia polycythemia sequence. These pregnancies account for about 20% of all twin gestations, and decades of experience with ART have shown us that monochorionic diamniotic gestations occur at a higher rate after in-vitro fertilization.
Although advances have improved the outcomes of multiple births, risks remain and elective MPR is still very relevant for twin gestations. Patients routinely receive counseling about the risks of twin gestations, but they often are not made aware of the option of elective fetal reduction.
We have offered elective reduction (of nonanomalous fetuses) to a singleton for almost 30 years and have published several reports documenting that MPR in dichorionic diamniotic pregnancies reduces the risk of preterm delivery and other complications without increasing the risk of pregnancy loss.
Most recently, we also published data comparing the outcomes of patients with monochorionic diamniotic gestations who underwent elective MPR by radiofrequency ablation (RFA) vs. those with ongoing monochorionic diamniotic gestations.2 While the numbers were small, the data show significantly lower rates of preterm birth without an increased risk of pregnancy loss.
Experience with dichorionic diamniotic twins, genetic testing
Our most recent review3 of outcomes in dichorionic diamniotic gestations covered 855 patients, 29% of whom underwent planned elective MPR at less than 15 weeks, and 71% of whom had ongoing twin gestations. Those with ongoing twin gestations had adjusted odds ratios of preterm delivery at less than 37 weeks and less than 34 weeks of 5.62 and 2.22, respectively (adjustments controlled for maternal characteristics such as maternal age, BMI, use of chorionic villus sampling [CVS], and history of preterm birth).
Ongoing twin pregnancies were also more likely to have preeclampsia (AOR, 3.33), preterm premature rupture of membranes (3.86), and low birthweight (under the 5th and 10th percentiles). There were no significant differences in the rate of unintended pregnancy loss (2.4% vs. 2.3%), and rates for total pregnancy loss at less than 24 weeks and less than 20 weeks were similar.
An important issue in the consideration of MPR is that prenatal diagnosis of chromosomal abnormalities is very safe in twins. Multiple gestations are at greater risk of chromosomal abnormalities, so performing MPR selectively – if a chromosomally abnormal fetus is present – is desirable for many parents.
A recent meta-analysis and systematic review of studies reporting fetal loss following amniocentesis or CVS in twin pregnancies found an exceedingly low risk of loss. Procedure-related fetal loss (the primary outcome) was lower than previously reported, and the rate of fetal loss before 24 weeks gestation or within 4 weeks after the procedure (secondary outcomes), did not differ from the background risk in twin pregnancies not undergoing invasive prenatal testing.4
Our data have shown no significant differences in pregnancy loss between patients who underwent CVS prior to MPR and those who did not. Looking specifically at reduction to a singleton gestation, patients who underwent CVS prior to MPR had a fourfold reduction in loss.5 Therefore, we counsel patients that CVS provides useful information – especially now with the common use of chromosomal microarray – at almost negligible risk.