What is the risk of miscarriage in the first trimester after IVF? The risk of miscarriage in the first trimester of pregnancy is estimated at between 10 and 20%. The true percentage of risk is not well known because many abortions occur before pregnancy is clinically recognized.
Data on miscarriages in spontaneous pregnancies are difficult to determine because this would require a systematic follow-up of large numbers of pregnant women through hCG and ultrasound tests. In the case of IVF or ICSI pregnancies, the pregnancy diagnosis is performed at an early stage and most women are motivated to follow their pregnancy closely. There are no robust data to compare the risk of miscarriage in spontaneous pregnancies versus IVF, but it is generally accepted that the risk is slightly higher after IVF.
The main reason for a higher risk of abortion is the age of the patients, which on average is 3 to 5 years longer than that of the fertile women in their first pregnancy. In fact, studies on the risk of spontaneous miscarriage indicate that maternal age is a major risk factor. There is clear evidence from oocyte donation programs that this risk is associated with aging of oocytes rather than by aging of the uterus. The risk of chromosomal aberrations in human oocytes increases from the age of 35 years and even more from 40 years of age.
When transvaginal ultrasound was started in the late 1980s, more detailed information was available than in the first weeks of pregnancy. One of the facts that could be observed in IVF pregnancies, with transference of 2 embryos, is that in about 30% of pregnancies, which in principle were twins, then became simple pregnancies, due to the death of one The two embryos. It is what is known as "evanescent twin".
The risk of miscarriage of a single fetus obtained by IVF is 30% in the first 6 weeks but falls to 10-20% at 6 weeks gestation when fetal heart activity is recorded. From 6 weeks of pregnancy, the risk of miscarriage after IVF decreases further reaching 2-4% over a 2-week interval and ending with a residual risk of stillbirth at 13 weeks' gestation of 2%.
Intrinsic abnormalities in the embryo are thought to be the main reason for failed conceptions or early miscarriages. The most important intrinsic factor contributing to embryonic loss are aberrations in the first meiotic division resulting in non-disjunction of homologous chromosomes and aneuploidies. The most frequent aneuploidies are trisomies of chromosomes 13, 15, 16, 18 and 21. It may be that in the future, preimplantation genetic diagnosis will reduce the time lost and the drama of abortions with embryos with aneuploidies. Many practitioners have observed an increased risk of fetal death and miscarriage in particular, as maternal age increases.
In IVF cycles, it is still an extended practice to transfer more than one embryo, in order to maximize the chances of a pregnancy. This practice translates into a high rate of multiple pregnancies. The results in terms of survival of twin pregnancies seem to be better than those of single pregnancies. The odds of complete abortion with twin embryos are around 5% while for single-embryo pregnancies, they rise to 20%.