Twin pregnancy, all you need to know

Since when do you see, who to follow, what are the risks and what is the prenatal path like? Here is a lot of useful information on twin pregnancy for a peaceful and conscious gestation

Twin pregnancy, when it is seen

“It is during the first trimester ultrasound , which takes place between 6 and 14 weeks, that the gynecologist checks the vitality of the embryo, the site of pregnancy (intra or extra uterine) and the number of fetuses present” he explains the expert.

The control of the Beta-hCG hormone , on the other hand, is not very indicative to understand if the pregnancy is twins : «The dosage of Beta-hCG is badly linked to the number of fetuses. A particularly high value of this hormone can in fact be caused by many factors, not only by the presence of more embryos in the uterus.

Twin pregnancy, the causes

«If the pregnancy is spontaneous, the presence of twins is quite rare: it occurs in less than 1% of cases . If, on the other hand, pregnancy is the result of an assisted reproduction procedure , then the chances increase. Even the familiar can play a role in the possibility of waiting for the twins . “

Familiarity concerns in particular the maternal line and is limited to heterozygous twins : it is probably linked to a predisposition of the woman to have double ovulation .

Twin pregnancy, the types

It is very important to understand as soon as possible that it is a twin pregnancy in order to evaluate what the type is.

«These gestations – explains Cavoretto – differ for several factors: the number of fetuses present; the number of placentas; the number of amniotic sacs and the possibility of having monozygotic or heterozygous twins. Depending on these variables, we intervene in a different way ».


1. The number of fetuses

Twin pregnancies generally have two or, more rarely, three fetuses . If they are spontaneous it is very difficult to exceed this number. In the past, ovarian stimulation procedures could also produce pregnancies with 5-6 fetuses, but now the techniques have improved and no more cases of this type are seen. Above three, in fact, the probability that they reach the end of pregnancy or develop normally is very low .


2. The number of placentas: monochorionic or bicorial twin pregnancy

«About 10% of twin pregnancies are monochorionic , ie there is only one placenta to which two or more fetuses are connected; the other cases are bicoric , ie there are two placentas for two different fetuses ».

“The first possibility is more risky – underlines the expert – because the fetal circulations are connected, so there is the possibility of blood transfusions from twin to twin”. In this case we speak of fetal-fetal transfusion , a condition that occurs in approximately one out of six cases and can be serious, life-threatening. If the situation is serious, we try to intervene with an operation to separate the placenta with a laser , or by anticipating delivery.

“Another complication of monochorionic pregnancy is selective growth retardation : one of the twins is smaller than the other, an element which, however, also puts the brother at risk.”

3. Amnioticity

We generally have one amniotic sac per twin. Very rarely (<1% of twin pregnancies) fetuses can be contained in the same amniotic sac as well as have a single placenta. These are very high-risk pregnancies, particularly due to the ease with which knots can form between the two umbilical cords, and require early counseling and management.

4. The zygosity

Twins can be monozygotic , that is to say they derive from a single fertilized oocyte that divides giving rise to two distinct individuals, or heterozygous , that is generated by two different oocytes fertilized at the same time by two different spermatozoa.

Monozygotic twins are genetically identical , while heterozygous twins are genetically different , just like siblings born of different pregnancies, so they may not look alike at all and may be of different sexes.

It is important to know the zygosity of twins to understand the incidence of some pathologies. In the case of monozygotic twins, if one fetus is affected by a genetic disease , the other will most likely be affected as well (unless they are diseases that depend on mutations arising after the division of the fertilized oocyte, which is quite rare) . In the case of heterozygous twins, however, the probability that both twins are sick depends on the type of inheritance of that disease: it is also possible that one is sick and the other healthy, exactly as it can happen with non-twin brothers.

Twin pregnancy, the prenatal path

For a bicorial twin pregnancy, the first and second trimester are very similar to those of a single pregnancy, also in terms of the type of tests to be performed, albeit with some peculiarities. In the third trimester , on the other hand, there are specific problems to face and generally some more checks »explains the gynecologist.

Monochorionic twin pregnancies , on the other hand, require checks every 2-3 weeks from the beginning of gestation to delivery, which on average occurs a few weeks earlier than bicorial twins.

Also with regard to prenatal diagnosis, the approach is similar to that of a pregnancy with only one child: “It is advisable to do the combined test of the first trimester , which involves the combination of nuchal translucency with a maternal blood sample for dosage of Beta HCG and PAPP-A proteins. Tests based on examination of fetal DNA circulating in maternal blood have limitations in twins: in particular they cannot identify which of the two fetuses is possibly affected by syndromes or malformations “.

Twin pregnancy, the risks

The risks of a twin pregnancy with two fetuses are increased compared to a single pregnancy, but are generally manageable. For the mother, there is an increased risk of developing gestational diabetes , hypertension, preeclampsia (especially if other risk factors are present) and cesarean delivery .

From the fetal point of view, there is instead a greater risk of spontaneous abortion , growth retardation and preterm birth . If the twin pregnancy is monochorionic, these risks are also added to those of fetal-fetal transfusion and fetal malformations : In monochorionic twins this risk increases by about four times, but it should be remembered that malformations are still rare events. 

Apart from this particular case, the risk of congenital malformations and diseases , including genetic ones, is equal to that of single pregnancies.

If a twin dies, in a bicorial pregnancy in general nothing is done except carefully observe the mother and fetus, making a correct planning of the birth and possibly prescribing an antibiotic therapy to avoid infections. 

If, on the other hand, the pregnancy is monochorionic the risks increase and advanced investigations may be necessary up to the anticipation of the birth. In theory, the earlier the abortion occurs, the more chances there are for the other twin to survive and have no problems .

Twin pregnancy and preterm birth

Generally speaking, the more the number of fetuses increases, the more the gestational period is reduced to delivery. There is talk of an average delivery time of 36-37 weeks for two fetuses, which drops to less than 32 weeks for triplets. With three fetuses, in fact, there is a very high risk of prematurity and mortality from prematurity .

In about 60% of cases, premature birth is spontaneous. “In a third of cases, however, it may be necessary to plan an induced birth or a caesarean following maternal or fetal problems. 

This occurs especially if the pregnancies are monochorionic, in which birth is almost always cesarean, or in the case in which hypertensive or gestotic problems occur ( preeclampsia), which involve the increase in maternal blood pressure and intrauterine fetal growth retardation.

Twin pregnancy, common ailments

A twin pregnancy is generally characterized by some elements: nausea at the beginning of gestation; hardening of the skin on the belly already from the second month; heartburn due to the pressure that children exert; digestive problems; shortness of breath and fatigue of circulation; water retention and the appearance of varicose veins .

Mothers have to prepare for nine months a bit complicated: “If the first two trimesters are quiet enough, the third is a bit more critical, especially for weight gain., which sometimes reaches higher levels than in a single pregnancy,

Furthermore, if there are two fetuses in the uterus, the energy demand for their growth will be greater and consequently the future mother may feel more fatigued.

If they do not have particular difficulties, future twin moms can safely work till the beginning of the eighth month. However, they generally have to stay at home a little earlier or, in some cases, even much earlier.

Twin pregnancy, childbirth

In general, twin births are a little more complicated than single births : The possibility of a vaginal birth is not excluded and only at the end of the pregnancy it is possible to evaluate whether to proceed in this direction according to the levels of well-being of the mother, fetal growth , position of fetuses and placenta. 

If these prerequisites are met, you can try, but it often ends up in a caesarean section anyway. In monochorionic pregnancies, on the other hand, there is a tendency to have an elective-planned caesarean section because there may be additional complications.

When is twin pregnancy seen? 

On the occasion of the first trimester ultrasound, which takes place between 6 and 14 weeks.

What are the causes of twinning? 

If the pregnancy is spontaneous, the presence of twins is quite rare: it occurs in less than 1% of cases. If, on the other hand, pregnancy is the result of an assisted reproduction procedure, the chances increase. Familiarity can also play a role in expecting twins.

What are the risks of a twin birth? 

The risks of a twin pregnancy with two fetuses are increased compared to a single pregnancy, but are generally manageable. For the mother, there is an increased risk of developing gestational diabetes, hypertension, preeclampsia and cesarean delivery.

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