Monozygotic twins-do they always have the same sex?

How are monozygotic twins formed?

A twin pregnancy occurs as a result of the division of an already fertilized egg cell. Monozygotic twins are otherwise known as monozygotic or monozygotic. This is because they are the result of the division of one zygote, which is formed from the fusion of one egg cell with one sperm. This division occurs within the first 14-16 days after fertilization. It is believed that if it occurs after 13. day after fertilization, incompletely separated twins are formed (so-called Siamese twins)

Monozygotic twin pregnancies carry a higher risk of complications than is the case with dizygotic twins. It is very important to recognize it early enough and have it monitored by a specialist, usually in a center with a III. degree of reference.

Monozygotic twins on ultrasound

The type of pregnancy should be diagnosed during the first trimester ultrasound. The test determines the number of chorionic villi and the number of amniotes. Based on these, the doctor can determine whether they are monozygotic or dizygotic twins.

Gynecologists are much more likely to divide twin pregnancies in terms of the aforementioned number of chorionic villi and amniotes. However, they do not use the division into monozygotic or dizygotic twins. If during an ultrasound in the first trimester, the doctor finds the so-called. Tau symptom means that the pregnancy is monochorionic. If, on the other hand, the Lambda sign is found-we are dealing with two chorionic villi. A singleton pregnancy means that the babies share one placenta, and thus complications can arise due to unequal sharing between the babies. 

Sex of monozygotic twins

Monozygotic twins, by virtue of having the same genetic material, have the same sex in most cases. Moreover, they look virtually identical. It is only their development after birth and the influence of the environment or surroundings that shapes the characteristics with which children may differ from each other in the future.

There are isolated reports of different sex in monozygotic twins. This is probably related to the fertilization of one egg cell by two sperm simultaneously. However, this is a very rare situation and still unclear to specialists.

Monozygotic twins-possible complications

A twin pregnancy is considered a high-risk pregnancy. Its most common complications include preterm labor, the death of one or both babies, birth defects, as well as stunted growth or pre-eclampsia.

Monozygotic twins are very often premature babies, and thus face the typical complications of babies born prematurely. These include necrotizing enterocolitis, retinopathy of prematurity and persistent ductus arteriosus.

Monozygotic pregnancies can be divided according to the time at which the zygote was divided into:

• bicaval bicaval pregnancy (i.e., 2 separate placentas and 2 amniotic sacs)
• monochorionic biparental pregnancy (68% of monozygotic twins)
• monochorionic singleton pregnancy

The latter is the least common, but child mortality is highest in its course, reaching up to 50%. This is due to the serious complications typical of singleton pregnancies. These include. TTTS, TRAP, TAPS or sIUGR syndrome. For this reason, from 16. Week of pregnancy ultrasound ex aminations for singleton pregnancies are performed every 2 weeks to be able to intervene in time if complications arise.

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Complications of multifetal pregnancies