So you’re pretty sure you’ve ovulated, and you and perhaps your partner have done your best to become pregnant – what now?
In the ‘average’ 28 day cycle, menstruation occurs on Day 1 and ovulation occurs at around Day 14. But remember, every woman and her cycle are unique
Many women get confused by the ‘Day 14’ terminology and assume that ovulation occurs fourteen days after menstruation has ended. Assuming an ‘average’ 5 days of menstruation, ovulation is more likely to be around nine days after menstruation has finished.
It is usually around fourteen days after ovulation, before menstruation starts again – however very few women have an ‘average’ cycle.
The luteal phase is the time after ovulation but before a period starts. It’s the longest-lasting phase of the menstrual cycle.
It is only possible to get pregnant for a short window of time after ovulation.
After ovulation – when the egg is released from the follicle – there is a period of between 12 and 48 hours when egg is in its best possible condition to be fertilised by a mature sperm.
Sperm can last for up to five days inside a woman’s body, sustained by the cervical mucous. Often, conception happens just after ovulation. If there are sperm already waiting in the fallopian tubes one will fertilise the egg after it has just been released.
Healthy, active sperm take around six hours after ejaculation to swim through the cervix and uterus, then into the fallopian tube to meet a waiting egg. For up to a couple of days after ovulation, it is still possible to conceive.
In any one menstrual cycle, there is generally only one fertile period. As levels of FSH (follicular stimulating hormone) rise, a number of follicles will develop in your ovaries, but usually just one will be released.
Because ovulation is triggered by a unique combination of hormones that rises and falls over the normal menstrual cycle, eggs can only be released from the ovaries during the 24-hour period when the ovulation-promoting hormones are at their peak. However, ovulation is not always precise or exact. Many babies have been conceived during windows of time which don’t fit within the average or “normal” fertile phase.
A pregnancy with fraternal twins results from two eggs being released from two different follicles. These eggs are fertilized by two separate sperm.
Around 4% of births are twins, but there are lots of factors which influence the rate of twins.
It is now thought that up to one in eight pregnancies may involve the very early fertilisation of more than one egg, but less than half of the second embryos will survive for more than a few weeks after ovulation. If the second embryo does not survive, it is reabsorbed by the woman’s body.
After ovulation, hormone levels decline and a feedback cycle triggers menstruation before the next ovulation.
For the next eight days or so after ovulation, the same events occur in your body whether the egg has been fertilised or not.
The follicle which released the egg grows larger and turns into a gland-like structure called the ‘corpus luteum.’ It then starts to produce the hormone progesterone, which causes the lining of the uterus (the endometrium) to grow thick and become covered with mucous that is produced by glands within the endometrium. This helps to prepare the lining of the uterus to sustain the fertilised egg.
After ovulation, if you are not pregnant, within around 48 hours, the egg moves along the fallopian tube, disintegrates and is absorbed back into the body.
The corpus luteum survives and continues to produce progesterone for around 12 to 14 days. After this, it dies (unless it receives the hCG hormone released from an embryo).
The level of progesterone in the body drops and the endometrium responds by shutting off its arteries, preventing blood from flowing to and from the surface of the uterine lining.
The blood that is already in the lining then pools lower in the uterus and the mucous-covered uterine lining, deprived of oxygen, dies back, the blood and lining seep into the vagina, so menstruation occurs and the cycle begins again.
After ovulation and until menstruation, your basal body temperature can remain about 0.5 degrees Celsius higher. Your cervical mucus becomes less slippery and more sticky or creamy in consistency.
The moment that one of the millions of sperm enters the outer surface of the egg, the egg’s coating changes so no other sperm can enter, the sperm and egg combine and form a ‘zygote.’
The zygote takes around five days to travel down the fallopian tube, with cells dividing and eventually forming a ‘blastocyst.’
Around eight to ten days after fertilisation, the blastocyst implants into the wall of the uterus.
Before implantation, there’s not a lot of change going on in your body, which behaves just as it would if you weren’t pregnant.
But after ovulation and then implantation, there’s lots happening. Sometimes there is a slight spotting or bleeding just after implantation – which some women mistake for a period.
But when the blastocyst attaches to the endometrium, becoming an embryo, various hormones are released which thicken the endometrium and help to seal off the cervix with a plug of mucous. This helps to reduce the risk of infection.
The embryo and placenta develop separately. After implantation, the placenta produces the hormone human chorionic gonadotropin (hCG). Within a few days, the level of hCG may be detected by a pregnancy test using the woman’s urine.
By Fran Molloy, journalist and mum of four