1. What Happens in Superfetation?
For superfetation to occur without assistive reproductive technology (ART), you would go through two menstrual cycles, back-to-back. Each cycle can lead to pregnancy. The scenario will be as follows:
In your first cycle, your body releases an egg, you have sex, and then the egg is fertilized and becomes an embryo.
The embryo implants in your uterine lining and starts to grow. In your next cycle, the same things happen and the new embryo joins the other embryo in your uterus.
This scenario is highly unlikely due to changes occurring in your body that prevent a new pregnancy once you are already pregnant.
2. What Causes Superfetation?
Superfetation is so rare that researchers do not have enough data and information to confirm its causes. Only a handful of these pregnancies have been documented. Most of them include assistive reproductive technologies that bypass some of your body’s barriers to back-to-back pregnancies.
3. What Prevents Someone Who is Already Pregnant from Getting Pregnant?
When you are pregnant:
. Your hormones change to prevent your ovaries from releasing another egg. The probability of ovulation during pregnancy is very low.
. A mucus plug forms in your cervix, making it difficult for sperm to enter your uterus. Your cervix is the opening between your vagina and uterus. If you were to have sex during pregnancy, sperm would have difficulty reaching your uterus and fallopian tubes, where fertilization occurs.
. Your hormones change to prevent the embryo from implanting in your uterine lining. Even if a second embryo were to form somehow, it is unlikely that it would be able to develop in your uterus.
4. Does Superfetation Have Any Complications?
The most important complication of superfetation is that babies are growing at different stages during the pregnancy. When one baby is ready to be born, another may not be ready yet. The younger baby is at risk of premature birth.
Premature birth puts the baby at higher risk for medical problems, such as:
. Respiratory problems
. Movement and coordination problems
. Low birth weight
. Brain hemorrhage, or bleeding in the brain
. Neonatal respiratory distress syndrome, a respiratory disorder caused by insufficient development of the lungs.
. Difficulties with feeding
Moreover, women who carry more than one baby are at increased risk of certain complications, including:
. Gestational diabetes
. High blood pressure and protein in the urine (preeclampsia)
The babies may need to be delivered by cesarean section (C-section). The timing of the cesarean section depends on the difference in the growth of the two babies.
5. Are Superfetation Twins?
No, but superfetation pregnancies are similar to twin pregnancies in some ways. Like twins, two fetuses eventually share the same womb and grow alongside each other. Usually both babies are born at the same time.
Unlike twins, embryos from superfetation don’t form during the same menstrual cycle. As a result, their gestational age is different (in different stages of pregnancy). The fetus that was conceived first matures earlier than the fetus that was conceived second.
6. How is Superfetation Diagnosed?
Superfetation can be difficult to diagnose since it may resemble other conditions involving twins. During a routine imaging procedure to check your pregnancy, your doctor will notice two or more embryos. One fetus will appear further along in its development (a different gestational age) than the other. Some researchers believe that superfetation is a misdiagnosis of other conditions, including:
. Placental insufficiency: The placenta is the organ in your uterus that provides nutrients and oxygen from the gestational parent to the developing fetus. With placental insufficiency involving twins, the organ is unable to provide enough nutrients to support the growth of both fetuses. As a result, they grow at different rates.
. Twin-to-twin transfusion syndrome: Twins unequally share the nutrients from their gestational parent. As a result, one twin receives too many nutrients, and the other receives too little. On imaging, the fetus that receives more nutrients will be larger than the other.
It is also possible that ultrasound errors lead to the misdiagnosis of a pregnancy involving twins as one involving a single fetus. Later, when the second embryo is discovered, the error could be chalked up to superfetation.
Read more about: Pregnancy After Being a Surrogate