Uterus Size May Predict Risk for Premature Twins After IVF

The size of a woman’s uterus can predict whether she is at risk of having very premature twins after IVF treatment, researchers have discovered.

IVF is a treatment given to women to increase their chances of getting pregnant. During treatment, a woman is given drugs to stimulate ovulation and her eggs are removed from the ovaries. The eggs are then combined with sperm in a laboratory, before being implanted back into the woman.

This new French study claims that by using ultrasound to measure the height of a woman’s uterus, doctors can predict whether or not she is at risk of having babies born prematurely if she becomes pregnant with twins after IVF.

The findings could help medical professionals and women make objective decisions about how many embryos should be transferred in one IVF attempt. 

“Twin pregnancies account for between a quarter and a third of pregnancies obtained during IVF, and 8% of them are complicated by the babies being born extremely premature, leading to medical complications and sometimes foetal mortality,” said Dr Raphaël Hirt of the Hôpital Antoine Béclère, Paris. 

Dr Hirt added that for this reason, single embryo transfer is promoted as the best way of avoiding twin pregnancies. However, in some cases, this can alter the overall likelihood of pregnancy.

“An evaluation of a woman’s individual risk of perinatal adverse outcomes from a twin pregnancy may help to select those women who have a lower risk of having twins born severely prematurely, and who could consider a double embryo transfer if that is what they want,” Dr Hirt advised. 

Women who already have children are less likely to give birth prematurely, probably because the uterine cavity has been distended by previous pregnancies. 

Dr Hirt and his team decided to see whether the height of the uterus, as measured by transvaginal ultrasound (a process called hysterosonometry or HSM) could predict the outcome of twin pregnancies after IVF.

The team measured the uteruses of 79 women who were receiving IVF treatment, dividing them into three groups according to uterus size. 

Women with the smallest uteruses (group one) were significantly more likely to have babies born severely premature, with an increased number of foetal deaths. The average gestational age of babies born in group one was just 33.7 weeks, compared to an average age of 37.5 weeks for the other two groups.   

There were seven foetal deaths in the first group compared with one in the second group and none in the third group. Six of the deaths in the first group were linked to being born prematurely, while the one death in the second group was not.

“This is the first time that uterine length has been used to predict which women are more likely to have twins born prematurely. Our results show that HSM is a reliable and non-invasive method for predicting twin-related severe prematurity and neonatal mortality,” said Dr Hirt. 

HSM can be used before conception to help with objective decision making about the number of embryos to transfer. 

Dr Hirt advised that for women with a HSM measurement of less than 62mm, a single embryo transfer is indicated, but in those with a longer uterine cavity, a double embryo transfer can be considered, if it is acceptable to the patients. 

He stressed that transvaginal ultrasound is a common, easy and inexpensive examination. Furthermore, it is already practiced in many fertility clinics and would not increase IVF costs. 

“Although we suggest that further, larger studies should be conducted, we believe that even with the restricted number of patients in our study, the results are dramatically significant and HSM could be included in the criteria that clinics currently use when advising about the number of embryos to transfer,” he concluded. 

Dr Hirt and his team will be using HSM as new criteria and will be studying whether this results in a significant decrease in foetal mortality. 

They are also planning to study the impact of a short uterine cavity on singleton pregnancies, to see whether it could help to identify those women who will need intensive neonatal care.

The research was presented at the 24th annual meeting of the European Society of Human Reproduction and Embryology in Barcelona.

Posted by : Goral Gandhi, MSc,

                   Laboratory Director,

                   Rotunda – Center for Human Reproduction (Pvt) Ltd

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