The birth of twins slows after tripling in the last 25 years

Postponing motherhood has been one of the great changes that advanced societies have incorporated in the last half century. With it, the parameters of conception have also been modified. At an older age, the difficulties to reach it increase and end up requiring assisted reproduction techniques that, thanks to the great demand, and therefore the greater experience of the professionals, have contributed strongly to the birth rate.

But in their evolutionary line, reproductive techniques have left in their wake a great ascending mountain of twin and trigeminal deliveries in recent years. According to data from the Institut d’Estadística de Catalunya (IDESCAT), from 1985 to 2009 this type of birth multiplied by three (from 596 to 1813), reaching 1,778 twin births and 35 triple births. As for the triples, it was in 2004 when a greater number was registered, with 51 trigeminal births.

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The IDESCAT graphs also confirm that the proportion of multiple births increases with the age of the mother. According to the 2018 birth figures -the latest available-, among women under 35 years of age, the frequency of multiple births is below the average, while 6.40% of births to women of more than 45 years – those that most require assisted reproductive techniques to get pregnant – correspond to multiple births.

“During the 90s the pregnancy rate was important above all else, so embryo transfer –of 3 and 2 embryos at the same time- was at the service of this need for pregnancy. You didn’t think of anything else, ”explains Dr. Dolors Manau. She is the head of the Assisted Reproduction Unit of the Hospital Clínic, which since the mid-1980s has been studying fertility problems and applying medical treatment and assisted reproductive techniques, both artificial insemination and in vitro fertilization to women up to 40 years of age.

According to Dr. Manau, to ensure conception, the increase in multiple births responded to the transfer of those 3 or 2 embryos at the same time. Hence, it has gone from 584 double births that took place in Catalonia in 1985, to 1220 in 2018. In Barcelona, ​​it went from 125 births of twins in 1985 to 263 in 2018.

Change of medical focus

“Starting in 2000, the concept of success changed in the mentality of the doctor – it was a turn that the Nordic countries started. Pregnancy was no longer sought in whatever way to achieve it. The success of the reproduction cycle is established as a child born alive, at term and healthy ”, points out Dr. Manau. “In a double pregnancy, the risk is multiplied in everything, it is a morbidity that you add to the mother,” he points out, so the inflection was led by reducing the number of transferred embryos and betting on a clear target on pregnancies of a single fetus.

The IDESCAT figures also bear witness to this aspect: “The normality and prematurity of childbirth is related to multiplicity. On the one hand, the percentage of dystopian deliveries – slow, laborious and difficult – increases with multiplicity, and on the other hand, the percentage of premature deliveries also increases with multiplicity. With data from 2018, it is observed that 9.6% of simple deliveries are dystocic, compared to 18.8% of deliveries in which there is more than one baby. Although 94.0% of deliveries are at term, in multiple deliveries (twins or trigemines) this percentage drops to 54.8%.

Vital precision

Two factors, then, have helped make that target in singleton pregnancies. The number of embryos is discriminated to avoid multiple pregnancies and technology is used to further increase the possibility of pregnancies with a single embryo. And, indeed, better techniques and a change in practice have reduced multiple births. After a temporary trend in recent years in which the percentage of multiple births grew continuously until reaching a maximum of 2.4% in 2014 – 1641 births of twins and 14 of triples-, the trend thereafter is its decrease.

The 1,220 twins and 18 triples born in 2018 represent 2% of multiple births compared to the 62,496 total births that year. “The peak of descent indicates that we already work in a different way, thanks to the fact that technically it has evolved,” says Dolors Manau from the Hospital Clínic.

Among the most significant advances is the use of “powerful incubators that allow embryos to be kept, not 3 days old as we used to do before, but up to five days old, with which they are stronger. Thus, instead of transferring 3 or 2 embryos, now one is enough ”, explains the doctor. “In addition, we have learned to better select the embryos, because we can do the ‘screening’ of aneuploidies (numerical chromosomal abnormalities), that is, they are chromosomally healthy. “You can do a biopsy of the embryo to determine everything that makes it the best to transfer, and then you do not have to risk with 2 or 3 embryos. Also cryopreservation techniques, vitrifying to protect fertility without loss neither by freezing nor by thawing, have contributed to greater successes on the way to pregnancy.

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“In general,” says Dolors Manau, “there is more demand for treatments and the first and main cause is the delay in pregnancy. Fertility is linked to the quality and number of eggs, which decrease with age. The other cause of the difficulties in achieving pregnancy is the seminal quality of men, which in recent years has seen its parameters worsen, due to the influence of multiple causes ”.

Fertility and assisted reproduction clinics

According to data from the Direcció General d’Ordenació i Regulació Sanitària del Departament de Salut, in 2019 there were 67 fertility and assisted reproduction clinics registered in Catalonia, 50 of them in the demarcation of Barcelona, ​​of which 36 in the city of Barcelona . The Santa Creu i Sant Pau (Fundació Puigvert), Vall d’Hebron and the Clínic hospitals are the only three hospitals in the public system in Catalonia authorized to perform in vitro fertilization procedures with women up to 40 years of age.

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