Fraternal twins are also called dizygotic twins. And the difference between fraternal and identical twins is that fraternal twins derive from two different eggs. Fraternal twins may be the same gender, they may have many of the same characteristics, but also may be very different from each other and, in fact, share half of their genes just like their sisters and brothers. It's important to recognize that the difference between fraternal twins and monozygotic, or identical twins, is that monozygotic twins result from the fertilization of a single egg with a single sperm and then during the embryonic development, or during the cell splits, those massive eggs split into two individuals, which later develop into two offspring.
They begin to store fat, and their lower airways are developing. They're growing more hair on their heads and taste buds on their tongues. Their bone marrow has started making blood cells. Testicles will descend into the scrotum of boy babies, and eggs are filling the ovaries of girl babies.
The lungs aren't working fully, but they're formed and developing. The babies may even respond to sounds — such as music or your voice — by moving. Your twins' brains are growing rapidly. Though they're sleeping most of the time with eyelids closed , they can open their eyelids, which now sport eyelashes.
They may even turn toward a light. Layers of fat are building up under their skin, smoothing it out. They can make grasping motions and suck their fingers, and you may feel them hiccupping. Their lungs are continuing to develop. The twins are growing quickly and continue to gain fat. All of their bones are formed but still soft. They're practicing breathing rhythmically, moving the amniotic fluid in and out of their lungs to help them develop.
They can open and close their eyes, and nails now cover your babies' fingers and toes. Their arms, legs, and torsos are filling out.
Some babies even have a full head of hair by now. At the same time, they're shedding the fine hair covering their bodies. Control of their body temperature is one of the very last things to develop, but they're getting better at it, thanks to their brain development. While their skulls will remain soft allowing for an easier delivery , their other bones are hardening. The average gestational age for twins at birth is 36 weeks.
Their lungs are well developed by 34 weeks, and all body systems are now functioning. They spend their last few weeks building fat layers and putting on weight and shedding most of their body hair. The vernix that waxy coating on their skin thickens, and body fat increases.
BabyCenter's editorial team is committed to providing the most helpful and trustworthy pregnancy and parenting information in the world. When creating and updating content, we rely on credible sources: respected health organizations, professional groups of doctors and other experts, and published studies in peer-reviewed journals.
We believe you should always know the source of the information you're seeing. Learn more about our editorial and medical review policies. How your fetus grows during pregnancy. American College of Obstetricians and Gynecologists. Multiple pregnancy. Cleveland Clinic. Fetal development: Stage of growth. Hiersch L et al. Differences in fetal growth patterns between twins and singletons. National Library of Medicine. Johns Hopkins. Twin pregnancy: Answers from an expert.
Trends and correlates of monozygotic twinning after single embryo transfer. Obstet Gynecol. National Organization for Rare Disorders. Twin-twin transfusion syndrome.
Updated Monochorionic monoamniotic twins: neonatal outcome. J Perinatol. Rapid prenatal diagnosis of aneuploidies and zygosity in multiple pregnancies by amniocentesis with single insertion of the needle and quantitative fluorescent PCR. Prenat Diagn. Washington State Twin Registry. Common misconceptions about zygosity. Noninvasive prenatal determination of twin zygosity by maternal plasma DNA analysis.
Clin Chem. Michigan State University. Twin zygosity. Your Privacy Rights. To change or withdraw your consent choices for VerywellFamily. At any time, you can update your settings through the "EU Privacy" link at the bottom of any page. These choices will be signaled globally to our partners and will not affect browsing data. We and our partners process data to: Actively scan device characteristics for identification.
I Accept Show Purposes. Table of Contents View All. Table of Contents. The Sex of the Twins. Blood Type. How They Were Conceived. Number of Placentas. Prenatal Diagnoses. Physical Similarities. Testing for Zygosity. The Different Classifications of Unusual Twins. Was this page helpful? Thanks for your feedback! Sign Up. What are your concerns? Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles.
Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Related Articles. Overview of Monozygotic Identical Twins. How Identical Are Identical Twins?
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