Until fairly recently, multiple pregnancies were not that common, so research around them is not extensive. But now that more people have access to assisted reproductive technologies (ART), twins are becoming more of an occurrence. Scientists are still in the early stages of deepening our knowledge about multiple pregnancies, but here is some of what we now know.
How long do twins gestate?
Statistically, half of women who are pregnant with twins give birth before term [1]. Of course, this means the other half carry their twins for the expected 37 to 40 weeks.
Some preterm twin births may be initiated by doctors, often in response to risks to either the babies or the mother. Some research suggests twins’ lungs develop faster, so the babies can breathe sooner and can be born earlier. However, studies show [2] that twins born at 38 to 40 weeks are healthier and more viable than those born at 34 to 37 weeks. Therefore, the best course is for twins to gestate for about as long as a single baby [2].
Can twins hurt each other in utero?
That is one of the main arguments for delivering twins early. Statistics show that if each twin has their own placenta, they won’t harm each other and will be healthier if born after week 37.
If they share a placenta, there is a risk that only one will survive, and it increases after week 34. Therefore, the mother is likely to receive additional supervision and care. If the babies share a placenta, it does not automatically mean that labor should be induced or that a C-section will be needed [3].
Are there ways to avoid preterm birth of twins?
Among the methods used to delay preterm labor, there is the use of progesterone (intramuscularly or vaginally) and suturing of the cervix. We now know these methods do not prevent early birth for twins; the progesterone doesn’t seem to make a difference compared to a placebo [1], and the suturing actually increases the risk of premature birth [4].
One potentially helpful method is using a pessary. A pessary is a prosthetic ring placed on the cervix. If it is placed on week 22 and removed on week 36, it can reduce the risk of preterm birth. However, there have only been two studies regarding its use, so it’s too early to draw conclusions about its proven effectiveness [4].
So, even with all of our advanced technologies, in the end, the likelihood of delivering twins early is still 50/50.
