What differentiates twin pregnancy from twins pregnancy?

Although in general terms it is understood as a twin pregnancy any pregnancy of two embryos, we should know that twins are not the same as twins. Visibly there is an important difference and that is that the twins are identical and of the same sex. In any case, both are considered risky pregnancies, since they present a higher probability of complications.

Double pregnancy is the most common form of multiple pregnancy, although there are also occasional occasions in which there are gestations of triplets, quadruplets, quintuplets ...

Below you have an index with all the points that we will discuss in this article.

Index

What differentiates twin pregnancy from twins pregnancy?

• 1. Types of twin pregnancy
• 2. Most common risks
• 3. Factors that favor multiple pregnancy
• 4. Symptoms of twin pregnancy
• 5. Twin pregnancy and assisted reproduction
• 6. Questions from users
• 6.1. What are the most prominent signs and symptoms of twin pregnancy?
• 6.2. How to get pregnant with twins or twins naturally?
• 6.3. When is a twin pregnancy detected?
• 6.4. What is the usual weight that a pregnant woman earns from twins?
• 6.5. Is the pregnancy of twins with a single placenta possible?
• 6.6. Is multiple pregnancy hereditary?

They are not the most common pregnancies, especially in a natural way, although they can occur more frequently after in vitro fertilization treatment when more than one embryo is transferred. However, reproductive medicine is trying to stop the proliferation of this type of pregnancy.

Types of twin pregnancy

Multiple pregnancy occurs as a result of different processes that, in addition, will determine the type of twins:

• Twins bivitellines or bicigóticos: occurs after the fertilization of more than one egg with different sperm. It is what we commonly know as twins (or triplets, quadruplets, quintuplets, etc.). The children have physical resemblance but as with any other brother. They may also have different sex, depending on the sperm that has fertilized. The case of twins is usually presented with a frequency close to 70% of multiple pregnancy cases.
• Identical, monozygotic or univitelline twins: arise from the division of the same embryo. Babies have the same genetic load, the same sex and a virtually identical physique. It occurs with a frequency of approximately 30% of cases of multiple gestations.

In turn, in the case of identical twins, we can make a classification based on the moment when the embryo was divided into two independent embryos. This will affect the placenta and the number of amnios or bags:

• Bicorial-biamniotic pregnancy: the division occurs in the morula embryonic stage, before the fifth day of embryonic development. Each of the embryos will develop into a placenta and an individual amniotic ball.
• Monochorial-biamniotic pregnancy: the fragmentation of the embryo takes place in the blastocyst stage (between days 4 and 8 of embryonic development). Drift in one placenta and two amniotic bags.

Types of monozygotic twins

• Mono-monoamniotic pregnancy: occurs when the division took place between day 8 and day 13 of development. In this case, both embryos share a pouch and a placenta.
• Siamese twins: the division occurs in an advanced stage of embryonic development and therefore is not complete. Both embryos grow in the same bag and the same placenta but in an anomalous way.

In the case of bicigotic or twin embryos, being two independent ovules, they will evolve in two placentas and separate bags. It is therefore bicorial-biamniotic pregnancy.

Most common risks

This type of pregnancy usually involves a series of risks for both the woman and the future baby. Below we summarize the most common:

• Premature delivery
• Low birth weight

Low weight incubator

• Preeclampsia
• Greater fluid retention
• Delayed intrauterine growth
• Gestational diabetes
• Chromosomal alterations: for this it is recommended to carry out genetic studies.
• Fetal-fetal transfusion syndrome: occurs when one fetus receives more blood than the other. It occurs in monochorionic pregnancies and can be serious, although detected early, it has a solution.

If you want more information about the possible risks, you can read this article: risks of multiple pregnancy.

Factors that favor multiple pregnancy

There are several factors that can favor the achievement of a multiple pregnancy such as:

• Hereditary: it is transmitted through the mother's side when the woman has a history of this type of pregnancy in the family. It can also be given if the father has a history of twins in the family but transmits it to the daughter. It is not true that this type of cases skip one, two or three generations, although it can happen.
• Age of the woman: when the woman exceeds 30-35 years of age at the time of pregnancy, there are more chances of multiple pregnancy. Hormonal alterations as menopause approaches may favor double ovulations.
• High body mass index (BMI): some studies indicate an increase in the probability of poliovulation in women with a BMI greater than 30.
• Assisted reproduction: Fertility treatments have been responsible for many of multiple pregnancies due to the artificial stimulation of ovulation and the transfer of more than one embryo. However, reproductive medicine is trying to stop this type of pregnancy.
• After the continued taking of contraceptive pills: some studies point to a possible rebound effect after taking the contraceptive pill.

Symptoms of twin pregnancy

Although the evolution of the twin pregnancy is practically the same as that of the single pregnancy, there may be slight variations in the symptoms.

Women with this type of pregnancy usually suffer more nausea and vomiting than in a single pregnancy. The size of the uterus in this type of pregnancy is also greater, which can generate more discomfort and a heavier feeling.

Therefore, it is important to follow the medical indications so that the twin pregnancy evolves month after month in a healthy way and allows the birth of healthy children.

Some common recommendations to reduce the possible risks and complications are:

• Rest: it is likely that the woman requires some additional tranquility to what is required in a single pregnancy.
• Comprehensive medical control: you should perform a greater number of ultrasounds and you should visit your doctor a little more than usual. An early diagnosis is important at the time of carrying out the pregnancy and planning the delivery (although it does not necessarily have to be this way, it is very likely that it is by caesarean section).

Once the children are born, the mother will need all the help she can to face the upbringing of two or more babies at the same time.

Twin pregnancy and assisted reproduction

In order to increase the chances of successful assisted reproduction treatment, two embryos are usually transferred in an IVF process. Thus, we increase the probability that at least one of them will implant and achieve pregnancy. However, there is a possibility that both implant and lead to the pregnancy of twins.

Currently there are many studies focused on reducing double transfers to reduce the likelihood of twin gestation without affecting the pregnancy rate.

Multiple pregnancy and in vitro fertilization

These investigations focus on the selection of the best embryo, which offers the greatest guarantees of implantation, thus increasing the probability of pregnancy with the single transfer.

When we associate multiple pregnancy with in vitro fertilization, we must bear in mind that we are talking about twins and not monozygotic twins, although we tend to confuse both terms socially. The case of identical twins in assisted reproduction could occur with the same probability as in a natural way.

You can read more about this in: assisted reproduction and multiple pregnancy.

Questions from users

What are the most prominent signs and symptoms of twin pregnancy?

Response by Fertility Madrid

An increase of the uterine volume takes place, reason why the diaphragm moves to the thoracic cavity, diminishing the respiratory capacity.

• Increase blood pressure
• Increase maternal heart rate (palpitations)
• Varicose veins appear and swell feet and ankles
• Increase hormone levels
• Increases salivation and constipation may appear

That is why in Fertility Madrid we are in favor of transferring a single embryo.

How to get pregnant with twins or twins naturally?

There is no way to place a twin pregnancy naturally, it will depend on the probability that a woman has to ovulate more than one ovule in the same cycle or the probability that the embryo will fragment and lead to the development of two independent embryos.

When is a twin pregnancy detected?

The pregnancy test analyzes the level of beta-hCG in maternal blood to confirm or rule out pregnancy. A level of beta-hCG in the first weeks of gestation very high suggests a double pregnancy, but the confirmation will be obtained when the ultrasound shows two gestational sacs or double beats.

What is the usual weight that a pregnant woman earns from twins?

In a single pregnancy it is recommended not to increase more than one kilo per month of pregnancy, although the usual is to increase about 10-12 kilos approximately. In the case of multiple pregnancies, the average weight that the pregnant woman acquires is between 12 and 17 kilos.

In any case, it will depend on each woman and each situation. It is important to receive medical advice and specialists in gestational nutrition to avoid an excessive weight gain that can lead to complications during pregnancy and childbirth.

Is the pregnancy of twins with a single placenta possible?

No, when the pregnancy is of twins and not identical twins, each one comes from a different embryo and therefore each one will develop its own placenta and its own amniotic bag.

It is what is known as bicorial-biamniotic pregnancy.

Is multiple pregnancy hereditary?

Although it is currently unknown the existence of a genetic basis that establishes the inheritance of the probability of having twins / twins, it is true that the fact that there are cases in the family increases the probability of having a multiple pregnancy. This occurs especially in the case of twins, as it is likely that the probability of ovulating is doubled.

If you want more information about the inheritance of twins and twins, I recommend this reading: twin inheritance.