SUPERFECUNDATION AND SUPERFETATION

Do you know that there is a biological explanation for the famous twins with different skin colors? The biology behind them is superfecundation.

WHAT IS SUPERFECUNDATION

 It is the fertilization of two or more ova from the same cycle by sperm from separate acts of sexual intercourse, which can lead to twin babies from two separate biological fathers.

There are two types of superfecundation:

1.    Homopaternal superfecundation: This is the fertilization of two separate ova from the same father, leading to fraternal twins.

2.    Heteropaternal superfecundation: This is a form of atypical twinning where, genetically, the twins are half siblings – sharing the same mother, but with different fathers.

Sperm cells can live inside a female’s body for up to five days, and once ovulation occurs, the egg remains viable for 12–48 hours before it begins to disintegrate. Superfecundation most commonly happens within hours or days of the first instance of fertilization with ova released during the same cycle.

Ovulation is normally suspended during pregnancy to prevent further ova becoming fertilized and to help increase the chances of a full-term pregnancy. However, if an ovum is atypically released after the female was already impregnated when previously ovulating, a chance of a second pregnancy occurs, although, at a different stage of development. This is known as superfetation.

Heteropaternal superfecundation is common in animals such as cats and dogs. Stray dogs can produce litters in which every puppy has a different sire. Though rare in humans, cases have been documented. In one study on humans, the frequency was 2.4% among dizygotic twins whose parents had been involved in paternity suits.

In 1982, twins who were born with two different skin colors were discovered to be conceived as a result of heteropaternal superfecundation. In 1995, a young woman gave birth to diamniotic monochorionic twins, who were originally assumed to be monozygotic twins until a paternity suit led to a DNA test. This led to the discovery that the twins had different fathers.

Superfecundation and superfetation are two different, but rare events related to conception:

1.    Superfecundation: This happens when there are twins from ovulation on the same day with two separate fathers. Two separate eggs are released. Fertilization happens during the same menstrual cycle, usually within less than 24 hours of ovulation. The woman had sex with two different men within 5 days before or on the day of ovulation. Superfecundation or heteroparental superfecundation is the term for twins with separate fathers.

2.    Superfetation: This happens if there is a second pregnancy from two separate ovulations; this is usually weeks apart. The second ovulation can occur weeks or even months after the first. Superfetation happens when a woman gets pregnant again after the implantation of one fetus. For this to happen the pregnant woman must ovulate after she is already pregnant. This egg must be fertilized by another sperm. Crazy right?

This can occur weeks or even months after the first egg is fertilized, and the result is that one fetus is more advanced in pregnancy than the other.

In summary, superfecundation refers to the fertilization of two or more ova from the same cycle by sperm from separate acts of sexual intercourse, while superfetation refers to the occurrence of a second pregnancy during an existing pregnancy, with the second ovulation occurring at a different time than the first.

CAN A WOMAN OVULATE DURING PREGNANCY?

Typically, a woman does not continue to ovulate during pregnancy. Once a woman becomes pregnant, her body produces high levels of certain hormones that stop the cycle of ovulation, preventing the release of more eggs. This is part of the body’s way of protecting the pregnancy and ensuring the best chance of a healthy full-term baby.

However, in very rare cases, a phenomenon known as superfetation can occur, where a second, new pregnancy can start days or weeks after the first one. This happens when an egg is released from the ovaries and gets fertilized, even though a pregnancy has already occurred. This is extremely rare in humans, with only a handful of cases reported in medical literature.

RISKS

Superfecundation and superfetation while rare, do carry some potential risks. The main risk associated with are the same as any multiple pregnancies: the possibility of preterm birth. If the two fetuses are at very different lengths of gestation, there is a risk for the younger one to be delivered prematurely. As there is a higher rate of twins being born at less than 37 weeks, this increases the risk for the younger twin.

In addition, women carrying more than one baby are at increased risk of certain complications, including high blood pressure and protein in the urine (preeclampsia), and gestational diabetes.

It’s important to note that superfecundation and superfetation are extremely rare, and these risks are not something that most people will ever have to worry about. If you have any concerns about your pregnancy, it’s always best to consult with a healthcare professional. They can provide you with the most accurate information based on your individual health circumstances.

DIAGNOSIS

A multiple pregnancy can be diagnosed using a combination of medical history, physical examination, and several tests. Here are some common methods:

1.    Medical History and Physical Examination: The healthcare provider may suspect a multiple pregnancy if the uterus is larger than expected for the dates in pregnancy.

2.    Pregnancy Blood Testing: Levels of human chorionic gonadotropin (hCG) may be quite high with multiple pregnancy.

3.    Alpha-fetoprotein Test: Levels of a protein released by the fetal liver and found in the mother’s blood may be high when more than one fetus is making the protein.

4.    Ultrasound: This is an imaging test that uses high-frequency sound waves to create images of blood vessels, tissues, and organs. Ultrasounds can be done with a vaginal transducer, especially in early pregnancy, or with an abdominal transducer in later pregnancy.

It’s important to note that these methods are not definitive, and the symptoms can vary from woman to woman. If a multiple pregnancy is suspected, the healthcare provider will use these tools to confirm the diagnosis.