Twice as many twins were born last year as in 1977. Many suspect artificial reproduction methods behind this rise. But these are only partly responsible for an increase in the number of twin births, because overall only slightly more than 15 percent of the parents of twins owe their children to the test tube. Nevertheless, at just under 40 percent, a not inconsiderable proportion of pregnancies induced by artificial insemination result in twin births. In the following this will be examined in more detail.
When pregnancy is possible only with medical assistance
In 2015, according to the German IVF Registry (D-I-R), e. V. 57.998 women treated in the course of artificial insemination. More than 2.5 percent of the children born alive (a total of 9.140 children) in 2014 after a so-called extracorporeal fertilization, Fertilization outside the body, born. This means that statistically in a large class at least one child was born due to artificial insemination.
In most cases, artificial insemination is used because pregnancy cannot occur naturally. Approximately one in six to seven couples cannot become pregnant without medical assistance – so-called assisted reproduction. The underlying causes are manifold, in the rarest cases there is complete infertility. The following causes are frequently observed:
- impaired sperm production and/or maturation due to alcohol, nicotine, unhealthy diet, obesity, overly extreme endurance training or certain medications such as antihistamines, antibiotics or anabolic steroids
- narrowed vas deferens as a result of a disease such as a chlamydia infection
- blocked epididymal tubules
- mumps disease in adolescence
- psychological causes such as psychosocial stress
- the reduction in the function of the ovaries that comes with increasing age
- genetic changes in the oocytes
- Dysfunction of the ovaries or the ovarian tubes
- Thickening of the secretion formed by the cervix (cervical mucus) due to nicotine consumption
- Benign growth of the endometrium (endometriosis)
- hormonal dysfunctions (u.a. polycystic ovary syndrome, thyroid dysfunction)
- basic immunological diseases
- Overweight or underweight
If these causes cannot be eliminated, a desire to have children can be realized in some cases by artificial reproduction methods. Before the connection between twin pregnancies and artificial insemination can be considered in more detail, a few things must be clarified in advance. This includes answering the question "How do twins develop??" as well as the distinction between identical and fraternal twins.
How twins are born?
Generally, a distinction is made between monozygotic and dizygotic or. mono- and dizygotic twins differentiated. And also the question "How do twins come into being??The question "How many eggs will be used to produce the twins?" must be answered depending on the so-called zygoticity, i.e. how many eggs will be used to produce the twins.
Monozygotic or identical twins are formed when the egg divides into two embryonic units after fertilization. Within the framework of this mechanism, which can be described as a "freak of nature", identical triplets, quadruplets or quintuplets can also be produced. In all these cases, the embryos carry the same genetic material, since they have emerged from the same fertilized egg (zygote) and are also phenotypically – in terms of appearance – confusingly similar. (Reading tip: How to live as an identical twin? An adult interview.)
The probability of twins is significantly higher after artificial insemination.
Timing of division is significant
In the case of identical twins, the decisive factor is at what point the fertilized egg divides into two embryonic units. Because a late date of division is associated with an increased risk of complications and malformations during pregnancy. If the egg cell divides within the first 24 hours after fertilization in the so-called two-cell stage, the two embryonic units each develop in their own amniotic cavity (amniotic sac), their own chorionic cavity surrounding the amniotic cavity and embryo, and with their own placenta (placenta). Such early division is rare, but is associated with a comparatively low risk in pregnancy.
If, on the other hand, division occurs after the egg cell has already divided several times (between the third and eighth day after fertilization), the so-called blastocyst (germinal vesicle) has already formed, in which the embryoblast lies, from which the later embryo develops. If this embryoblast divides in this stage – the so-called blastogenesis – into two embryonic plants, these must divide accordingly later both chorion cavity and placenta. If the embryoblast divides early within this phase, two amniotic cavities will develop. In most cases, the cell division that leads to the development of twins occurs at this exact stage of pregnancy. If the egg has already nested in the uterus (between the eighth and tenth day), the later embryos also divide the amniotic cavity. Twin pregnancies resulting from cell division late in blastogenesis are rare (1 percent) and must be monitored very closely during their development in the womb because the risk for complications is greatly increased.
In some cases, the division occurs at a much later stage (14. up to 15. day after fertilization) take place. At this point, the embryoblast can no longer divide completely, which is why both embryonic systems cannot separate completely and may have organs that are created together (Siamese twins).
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Two-egg or. Dizygotic twins share 50 percent of the genetic material, just like "normal" siblings. Because here, during one cycle, instead of one, two eggs are released from the ovary and each of them is fertilized by a spermatozoon. This can happen at the same time or up to a few days after each other. Although the eggs released from the ovary are only capable of fertilization for 6 to 24 hours, sperm can survive in the woman’s body for at least 48 hours on average – without losing their ability to fertilize. The fertilized eggs subsequently nest in the uterus and develop into fraternal twins, usually in separate amniotic and chorionic cavities and with two placentas. If the fertilized oocytes are in close proximity, the two placentas can also grow together. Conjoined twins have corresponding phenotypic similarity to simple siblings and may also have a different sex. They are much more common than identical twins, which account for only one-third of all twin births. (Reading tip: At some point, fraternal twins are also just siblings)
special case: polar twins
The so-called polar twins represent a special case. The eggs, which are stored in the ovaries and are still immature, go through two stages of maturation following ovulation and during their migration to the uterus before they finally become fertile. In this case, a polar corpuscle is released from the egg cell, which contains all the genetic information, but is not normally capable of development and dies in utero. In extremely rare cases, the polar corpuscle receives a part of the supplying cell body from the dividing egg cell, d.h. the general cellular environment with cytoplasm and organelles. They remain viable and can mature into a fertilizable egg cell in the same way as a "normal" egg cell. The two fertilized eggs contain the same genetic information on the mother’s side, but different genetic information on the father’s side, because they have been fertilized by two different sperms. They develop like fraternal twins, but look more similar to each other than to twins.
Guide to twin pregnancy
Small miracles: twins!
What does it look like in triplets and quadruplets??
In triplets and other multiples, there is usually a combination of monozygotism and polyzygotism. In rare cases, several eggs can be released from the ovaries at the same time and subsequently fertilized by sperm (triple and multiple pregnancy). In addition, simultaneous ovulation of two eggs with subsequent division of one (triplets) or both eggs (quadruplets) can result in a combination of identical and fraternal twins. (Reading tip: How to raise twins and triplets without ending up in the loony bin)
What are the risks associated with a twin pregnancy??
No one should get scared now: There are, of course, completely unaffected and complication-free twin pregnancies, like this one. But: A twin pregnancy is usually classified as a high-risk pregnancy, because it is a 20-fold increased obstetric risk presents. However, this classification does not mean that there is something wrong with the children or the mother. Rather, it serves to detect possible complications at an early stage through particularly close-meshed examinations. These complications include:
- High blood pressure and excretion of protein in the urine (preeclampsia),
- Lower placenta with painless bleeding (placenta praevia),
- premature rupture of the membranes with risk of premature placental abruption,
- too little (oligohydramnios) or too much amniotic fluid (polyhydramnios) in one or both amniotic cavities, (for example, due to premature rupture of the membranes or cervical insufficiency),
- Growth restriction (Intrauterine growth restriction),
- Umbilical cord strangulation,
- increased perinatal morbidity and mortality,
- Positional anomalies and
- Decreased contraction of the uterine muscles (uterine atony).
In twin pregnancies, premature birth often occurs as a result of premature rupture of the membranes or cervical insufficiency. Also, the more children that develop in utero, the more the average gestation period shortens from 40 weeks for singletons, to 37 for twins, 35 for triplets, 33 for quadruplets, etc. What is generally significant is how the twins can be cared for in the uterus. For favorable care, it is again crucial that the children grow in their own amniotic cavity (amniotic and chorionic cavity), each with an independent placenta. On the other hand, conditions are less favorable if the two children have to share both the amniotic cavity and the placenta.
Here the risk of complications also increases. Among other things, there is a risk of so-called fetofetal transfusion syndrome (FFTS), in which differences in blood pressure between the embryonic circuits cause blood to be channeled from one twin (donor) to the other (recipient). This leads to developmental delays in the delivering child, while the other child develops virtually at its expense. Since mostly identical twins sharing chorionic cavity and placenta are affected by this syndrome, twins created by an artificial reproduction method and therefore mostly fraternal are less likely to have it.
Artificial insemination usually results in fraternal twins
Most twin pregnancies in Germany occur naturally. Nevertheless, the probability of having twins is increased with artificial insemination, but it depends fundamentally on the choice of the method selected. For example, up to three embryos can be transplanted into the uterus during so-called in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI) and cryotransfer in accordance with the German Embryo Protection Act in order to increase the success rate. Here, several eggs are transferred, each of which can develop into an embryo and thus into fraternal twins or triplets.
Division of a single egg with development of monozygotic twins is possible, but with 1.5 % (IVF), 1.6 % (ICSI) and 2.2 % (cryotransfer) according to the German IVF Registry (D I R) rather unlikely. Thus, according to DIR 2014, as a result of the above three methods of reproduction, 9.479 singletons, 2619 twins, 74 triplets and 3 quadruplets were born. In percentage terms, this corresponds to 77.9 % for singletons, 21.5 % for twins, 0.6 % for triplets and 0.03 % for multiples. More than one fifth of the pregnancies induced by these methods are twin pregnancies. However, these averages shift slightly depending on age, the number of eggs transferred, and the actual method of fertilization chosen.
With intrauterine insemination (IUI), in which the sperm prepared in advance is injected into the uterus, the probability of a twin pregnancy is statistically just as high as with "natural" fertilization. In some cases, however, hormonal stimulation is carried out in advance to promote the maturation of the eggs. And it is precisely this hormonal stimulation that has led not only to an increase in twin pregnancies in recent years, but also to the spectacular multiple births with seven, eight or nine children. Meanwhile, following hormone treatment, ultrasound is used to determine how many mature eggs are ready for fertilization in the fallopian tubes and uterus. Accordingly, the probability of an (unwanted) twin birth is also extremely low here. Many couples nevertheless take a chance, as they have already been waiting a long time for a pregnancy.