| Twins can be the same (identical-monozygotic) | | | | years of age is less than half of what it |
| or different (fraternal-dizygotic). Fraternal | | | | would be after the age of 35. 2. You are more |
| twins, triplets, or more develop when two or | | | | likely to conceive twins in the first few |
| more eggs are fertilized by separate sperm. | | | | menstrual cycles after stopping birth control |
| Fraternal fetuses have separate placentas and | | | | pills. 3. Infertility treatment. Fertility |
| amniotic sacs (the bag containing the fluid | | | | drugs stimulate your ovaries to release |
| around a baby). Identical twins come from a | | | | multiple eggs, which can be fertilized at |
| single egg that has been fertilized by one | | | | once. This may result in a multiple |
| sperm. For unknown reasons, the fertilized | | | | pregnancy. You are, therefore, more likely to |
| egg splits into two or more embryos during | | | | have a multiple pregnancy if you use |
| the first stage of development. Some | | | | fertility drugs or assisted reproductive |
| identical twins share the same placenta. | | | | technology (ART - In Vitro Fertilization |
| However, they usually grow within separate | | | | IVF). 4. ART is the transfer of embryos |
| amniotic sacs in the uterus. In rare cases, | | | | directly into the uterus. In the early days, |
| identical twins share one amniotic sac | | | | when success rates were extremely low, |
| (monoamniotic). Fraternal multiples: 1. Can | | | | several embryos were transferred in the hope |
| be of different sexes and may have different | | | | of achieving a pregnancy. Nowadays, 25% to |
| blood types. 2. They may look very different | | | | 30% of pregnancies from ART are twins; 5% are |
| from one another, with different-coloured | | | | triplets and less than 1% are quadruplets or |
| hair and eyes. They may also look alike, as | | | | more. As techniques have improved, success |
| siblings often do. 3. Tend to run in | | | | rates from IVF/embryo transfer have increased |
| families. 4. They are more common in older | | | | and reasonable success rates are being |
| mothers, African races and when there is a | | | | achieved with single embryo transfer and this |
| family history of twins. They are least | | | | reduces the incidence of multiple |
| common in Asian families. If you have already | | | | pregnancies. What is the prevalence of |
| carried fraternal twins, you have double the | | | | multiple pregnancy? The natural incidence of |
| usual risk of having twins. A history on your | | | | twins is 1 in 80 pregnancies and for triplets |
| partner's side of the family does not | | | | 1 in 8000 pregnancies. The incidence is |
| increase your risk of multiple pregnancy. | | | | rising as a result of IVF and a tendency for |
| Identical twins 1. Are always the same sex | | | | women to deliver later in their reproductive |
| and blood type. 2. They do not necessarily | | | | years. Naturally occurring quadruplet births |
| look exactly alike. One may be right-handed | | | | occur in 1 per 600,000 births. The UK would, |
| while the other is left-handed. 3. They | | | | therefore, expect one set of naturally |
| develop at random. They are not related to | | | | occurring quadruplets each year. There are |
| maternal age, race, or family history of | | | | estimated to be approximately 125 million |
| twins. 4. Multiples that are conceived with | | | | human twins and triplets in the world, and |
| infertility treatment are usually fraternal, | | | | just 10 million identical twins. One in two |
| rather than identical. What are the causes of | | | | pregnancies with same sex babies are |
| multiple pregnancy? 1. With increasing | | | | monozygous (identical twins). The rate of |
| maternal age the chance of twins increases. | | | | identical twins remains at about 1 in 333 |
| To put it in perspective, your chance of | | | | pregnancies across the globe. |
| giving birth to twins if you are less than 25 | | | | |