How much sperm is needed for twins?
To form identical or monozygotic twins, one fertilised egg (ovum) splits and develops into two babies with exactly the same genetic information. To form fraternal or dizygotic twins, two eggs (ova) are fertilised by two sperm and produce two genetically unique children.
Some fertility drugs work by stimulating a woman's ovaries, which can sometimes cause them to release more than one egg. If sperm fertilizes both of these eggs, this can result in twins. In vitro fertilization (IVF) can also increase the chance of conceiving twins.
Monozygotic (MZ) twins, also called identical twins, occur when a single egg cell is fertilized by a single sperm cell. The resulting zygote splits into two very early in development, leading to the formation of two separate embryos.
Factors that increase the chance of twins include: consuming high amounts of dairy foods, being over the age of 30, and conceiving while breastfeeding. Many fertility drugs including Clomid, Gonal-F, and Follistim also increase the odds of a twin pregnancy.
Several factors for causes of embryo splitting were suggested, including maternal age, prolonged embryo culture, ovarian stimulation, and zona pellucida (ZP) manipulation .
Women who are over age 30 — especially women in their late 30s — have a greater chance of having twins. That's because they're more likely to release more than one egg during ovulation than younger women. Mothers between ages 35 and 40 who already have given birth have an even higher chance of conceiving twins.
Clomid (clomiphene), a pill taken by mouth to induce ovulation, causes twin pregnancies between 5% and 12% of the time. 1 That's fewer than one in 10 pregnancies. Your odds of conceiving triplets (or more) on Clomid is even lower: less than 1% (less than one in 100 pregnancies).
This is why fraternal twins run in families. However, only women ovulate. So, the mother's genes control this and the fathers don't. This is why having a background of twins in the family matters only if it is on the mother's side.
Even though only one sperm is needed for fertilization, most sperm cells will not survive the journey from the testicle to the uterus. Of the 200 million sperm deposited near the cervix in an average ejaculation, only 100,000 make it to the womb.
No. Only one ovulation can happen per cycle. You can, however, ovulate two (or more) eggs at the same time. When this happens, there is the potential to conceive fraternal (non-identical) twins if both eggs are fertilized.
Can you have twins if it doesn't run in your family?
Everyone has the same chance of having identical twins: about 1 in 250. Identical twins do not run in families. But there are some factors that make having non-identical twins more likely: non-identical twins are more common in some ethnic groups, with the highest rate among Nigerians and the lowest among Japanese.