Conception occurs when a woman’s egg meets a man’s sperm, and the two melt together to form the first cell in a new human being. This is familiar knowledge to most of us.
But what, exactly, happens next? A lot of interesting things, as we shall see.
Most of what follows is stuff you don’t need know in order to get pregnant. If you had sex around the time of ovulation, you did your part. Everything that happens from then on, nature will take care of on its own.
If you like to understand how things really work, however, or just want to marvel at the miracle of life: read on.
Ovulation and fertilization
For natural conception to occur, an egg cell must be released from one of the woman’s ovaries in the process known as ovulation, and fertilized by her partner’s sperm.
Healthy women ovulate approximately once a month. When the egg cell has been released, it must be fertilized by a sperm cell within 24 hours, perhaps even less. Otherwise, it dies, and your chances of conception are gone until the next cycle.
This means that the window for conception is very short: it can only happen during a brief 24-hour period every month.
Luckily, sperm cells can live for a few days inside the woman. This is why, when you want to get pregnant, it’s important to plenty of sex right before ovulation. It will ensure that there’s a good supply of fresh sperm waiting, ready to fertilize the egg as soon as it’s released.
Every time the male partner ejaculates, millions of sperm cells are released. Only a handful, however, will ever reach the egg. And only a single sperm cell will finally penetrate the egg and fertilize it.
In this magical moment, the genetic material of the two cells combine to create a new cell: the beginning of a new life.
Cell division (cleavage)
When the egg and the sperm melt together, they first form a single cell called a zygote.
The new cell rapidly divides itself into two cells, which again divide themselves into four cells, then eight, and so on. This process is called cell division or cleavage.
The new cells form a cluster called a blastocyst. For the first few days after fertilization, the blastocyst continues to divide and grow while it travels through the fallopian tube, a very fine tunnel which connects the ovary to the uterus.
The video below describes this process in detail:
You’re not actually pregnant until the blastocyst has implanted, which means that it attaches itself to the inner wall of the uterus.
This happens between 6 and 12 days after ovulation. The most likely implantation day is 9 DPO (days past ovulation). The blastocyst now becomes an embryo.
Once it has implanted, the embryo starts to produce a hormone known as hCG (human chorionic gonadotropin). This is the hormone which is detected by pregnancy tests and makes them turn positive.
For the first few days after implantation, the level of hCG is too low to be detectable, but it doubles every 2-3 days.
hCG levels vary a lot from woman to woman and from pregnancy to pregnancy, but a blood test can typically confirm pregnancy 3-4 days after implantation. A sensitive urine test will be positive 4-5 days after implantation.
Read more: 10 tips for getting pregnant faster
Frequently asked questions about conception
Q: Where does conception occur?
A: The egg and the sperm meet and melt together in the fallopian tube. After ovulation, the egg’s journey from the ovary to the uterus through the fallopian tube takes several days. When it reaches the uterus, it’s too late for it to be fertilized.
Q: When conception occurs, can you feel it?
A: The scientific answer is no, you can’t actually feel conception.
When the egg cell is fertilized, it’s floating freely in the fallopian tube. Nothing connects it to the mother’s body yet, and the hormonal changes that occur immediately after ovulation are the same whether the egg was fertilized or not.
Once the egg has implanted, on the other hand, it will trigger the production of the hCG hormone. This, in turn, leads to other hormonal changes that are different from non-conception cycles. Some women can experience very early pregnancy symptoms at this point, but it’s probably more common not to notice anything different at all before you miss your period.
That being said, any fertility forum has plenty of stories from women who say they felt pregnancy symptoms, or “knew” they were pregnant, before implantation — sometimes immediately after conception. They often argue that conception will trigger “chemical changes” that a woman in tune with her body can perceive, despite the fact that the fertilized egg is not yet attached to her.
Whether you believe this sort of intuition is possible or not is up to you, but there’s currently no scientific evidence that conception can be physically felt.
Q: Does alcohol affect conception?
A: The frustrating answer to this question is “maybe”.
Did you drink alcohol on ovulation day, and want to know if it reduced your chances of conception in this cycle? It probably didn’t matter much. What you eat or drink on any single day isn’t likely to have much impact. People get pregnant when drunk all the time.
Can regular drinking reduce your fertility in general? Yes, indeed, but nobody knows how much alcohol it takes.
Heavy drinking definitely reduces fertility, both in women and men. Some studies conclude that moderate and even low alcohol consumption can reduce fertility, too, while others find no correlation. There’s currently no consensus on a “safe limit”.
What is well known, however, is that alcohol during pregnancy can very seriously harm the baby, and that the fetus is most vulnerable to exposure during the first 12 weeks of pregnancy.
Because alcohol can affect the embryo before the pregnancy is confirmed, most countries’ health agencies recommend that women don’t drink alcohol at all while they are trying to conceive.
Q: Does caffeine affect conception?
A: As with alcohol, research on caffeine and fertility looks at long-term effects. If you binged on coffee or caffeinated soda on ovulation day, it probably didn’t impact your chances of conception if you’re otherwise a moderate caffeine consumer.
A recent meta study found no clear association between caffeine consumption and natural fertility, measured by “time to pregnancy”. Similarly, caffeine consumption didn’t seem to have any effect on the success rate of fertility treatments.
On the other hand, more than 300 mg of caffeine per day seems to be associated with a significantly increased risk of spontaneous abortion. Multiple studies have found that if either partner (yes, the man too) drinks more than three caffeinated beverages daily, it increased the risk of pregnancy loss.
One study found, however, that if the woman took a multivitamin supplement, this risk was dramatically reduced.
To err on the side of caution, you may want to reduce your caffeine consumption to two daily beverages or less, and to take a multivitamin supplement.
Q: Does running affect conception?
A: If you’re worried that running or other intense exercise will somehow prevent the egg from being fertilized or from implanting, relax. The human body is built for movement, and even intensive exercise will not prevent the sperm from reaching the egg or cause the fertilized egg to “fall out”.
On the contrary, regular exercise is great for your fertility — with one caveat.
Very hard exercise on a regular basis can cause an energy deficit, which in turn can disturb your menstrual cycle. Some top-level female athletes lose their menstrual cycle completely, which is unhealthy for many reasons. But even if you still get your period, you may not be ovulating, or your luteal phase may be too short.
If your exercise routine is intensive and you worry about it affecting your fertility, we recommend that you measure and track your basal body temperature every day. This will enable you to confirm that you are indeed ovulating, and that your luteal phase is sufficiently long.
Q: Does traveling affect conception?
A: If your travels put a distance between you and your partner during the fertile window, it will definitely reduce your chances to conceive. Otherwise, traveling is not likely to interfere with the conception process. How many couples haven’t conceived while on their honeymoon?
Very stressful traveling, especially if it involves jet lag, may delay ovulation in some cases. Use ovulation kits, keep having frequent intercourse, make healthy food and beverage choices when you can, and enjoy your travels.