I got the following question in my mail today:
"Hi, I'm in the process of going through donor egg after many failed IVF cycles. My doctor has advised that we have 2 embryos transferred but I am concerned of the risks - mainly of health issues that can occur from delivering premature babies which is usually the case with twins."
Tough question. I looked up the research that's been done on the topic and found the following review of research from The Cochrane Library, Issue 1, 2006(http://www.cochrane.org/reviews/en/ab003416.html):
In simple terms, when transferring two embryos you raise both the likelihood of achieving pregnancy and the likelihood of twins. Following is a quote with the statistical data removed:
"The clinical pregnancy rate per woman/couple associated with two embryo transfer was significantly higher compared to single embryo transfer. The live birth rate per woman/couple associated with two embryo transfer was also significantly higher than that associated with single embryo transfer. The multiple pregnancy rate was significantly lower in women who had single embryo transfer. "
In the research led by Dr. Ann Thurin, from Sahlgrenska University Hospital (http://www.brightsurf.com/news/june_04/ESHRE_news_063004_b.php) the transfer of single embryos (SET) was compared to double embryo transfer (DET) and the rate of pregnancies after the transfer of two embryos was not very different (39.7% vs. 43%). However, many of those opting for SET had to go through an additional frozen transfer cycle to transfer the second embryo.
With regard to twin prematurity, in a French study (Rufat et al., 1994) of 1263 IVF pregnancies, the prematurity rate (less than 37 weeks of amenorrhoea) in twins was 43.8% compared with 12.2% in singletons, the corresponding figures were 13.9 and 2.9% for extreme prematurity (less than 33 weeks of amenorrhoea). Indeed, at least according to this study, having a twin pregnancy more than triples the risk of prematurity. In this article - (the abstract is in English, the article in French), there's some good news - early diagnosis of twin pregnancy by ultrasound and subsequent treatment (resting at home and regular clinical examination of the cervix) was successful in reducing the rate of prematurity.
When I was going through IVF (Rachel's story), it was common to transfer 4 embryos, which I did 4 times. Two of those cycles failed, one resulted in the birth of a singleton and one in the development of three sacs - 2 of which became embryos and resulted in the birth of twins. In my last IVF cycle, I transferred two embryos and became pregnant with a singleton (I later miscarried due to a large uterine hematoma).
My experience was that carrying twins was a bigger strain on the body. During my twin pregnancy I was much more susceptible to illness and even spent a few miserable days in the hospital hooked up to an IV after I came down with a mysterious (non-pregnancy related) virus in my mouth. I was lucky to have an uncomplicated pregnancy that continued through the 39th week, when my doctor decided to strip my membranes to induce labor.
Carrying twins, of course, is not the only issue. Once they're born, you have two babies to take care of... quite a challenge. I read this very insightful blog entry on Infertility Is Funny. I think she captured well what being a new mom is like. Multiply that (at least) times two if you're thinking of twins...
The decision of how many embryos to transfer is not an easy one. I think today I'm actually glad I didn't have all the information in front of me when I made my decision.