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Only a tiny fraction of the sperm that entered the vagina make it to the fallopian tube (5). That means that only one of the two fallopian tubes will have eggs, and some sperm will have gotten it wrong. The vast majority of the time, a person only releases one egg from one ovary. Once sperm enter, the number of white blood cells increases, and they begin to attack the dying sperm, though it’s possible they may also attack healthy sperm too (1,5).Īlso, sperm may end up going up the wrong fallopian tube. Sperm triggers an immune response when it enters the uterus (5). The uterus also has little finger like structures called cilia that help move the sperm, hopefully, towards the egg (1). Sexual activity can cause the brain to release the hormone oxytocin (1,6), which causes the innermost layer of the uterus to contract and push the sperm onwards (1,5,6). (With artificial insemination, sperm is often introduced directly into the cervix or uterus, so this step is bypassed.)Īlthough sperm use their tails to swim through cervical mucus in the vagina and cervix, it’s actually the uterus that moves sperm through it and into the fallopian tubes (1). If a person has unprotected penis-vagina sex during their fertile window, probably at least some sperm will make it’s way through the cervix and into the uterus.

In response to increasing levels of progesterone:Įndometrial cells stop dividing and start growing largerĪlso, the rise in progesterone after ovulation also signals to the endometrium to release little sugar-filled sacs into the uterus to nourish the incoming egg (2). Estrogen causes the lining of the uterus to thicken by stimulating the endometrial cells to divide (2).Īfter ovulation, the endometrium prepares for the possible arrival of a fertilized egg. After shedding, the endometrium waits for estrogen (produced in the ovaries) to rise. How the uterus prepares for pregnancyĭuring your period, the uterus sheds the endometrium, which built up during the previous menstrual cycle. When exposed to sperm, the vagina becomes less acidic (1,5). Normally the vagina is somewhat acidic, in order to protect against infection (5). In the instance of sexual interactions, sperm have an effect on the vagina. The time period between when cervical fluid is ideal for sperm and ovulation is known as the fertile window. Ovulation is when an egg is released from the ovary, and is critical to the whole process. How ovulation worksīefore diving into conception, you should brush up on your knowledge of, and of how ovulation works. It’s possible some of this information will change in the future. Some of this information might also apply to conception that happens with the help of artificial reproductive technologies like in-vitro fertilization (IVF), though we don't directly focus on that topic here.Īlso, FYI, a lot of this information is based on animal research, especially events that happen deep in the reproductive tract. Here, we’ll talk through what different parts of the body are doing at different times to prepare for pregnancy when it occurs from penis-vagina sex or from other forms of insemination, such as artificial insemination. While that is the bare bones of how conception works, there’s a lot going on in a person’s body that helps-or sometimes hinders-conception. Sperm meets egg, egg meets uterus, and boom: pregnancy. This is what most of us learn about how a pregnancy happens: It takes about 6-12 days for the fertilized egg to travel to the uterus and attach to the uterus in a process known as implantation Only a tiny fraction of the sperm that entered the vagina make it to the fallopian tube

It's much more complicated than “sperm meets egg”