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Normal Pregnancy

Please remember that the first day of the menstruation / bleeding is counted as DAY ONE, second day as DAY TWO and third day as DAY THREE and so on. This will avoid any confusion in your history and treatment when you are asked to start your medication, or come to the clinic for hormone test or ultrasound scan on a certain day of the cycle.

A pregnancy results by fertilization of an egg by a sperm and implantation of the resulting embryo to the lining of the uterus. There are around one million immature eggs in the ovary of a baby girl when she is born. Every month two to three eggs will start growing in the early part of the menstrual cycle but normally only one will become mature.

Pregnancy Process

For the whole reproductive life of a woman only around 500 eggs are required assuming that a woman will start menstruating at the age of 15 and stop menstruating at the age of 50 , and only one egg is liberated from the ovaries every cycle ( every month ). The eggs grow within the ovaries in small fluid filled cysts called follicles. They appear like small cysts ( black in colour on an ultrasound scan). Even though several follicles start to grow in the early part of the menstrual cycle, only one will reach maturity. The other follicles shrivel up and do not produce eggs.

The follicles grow under the influence of hormones produced by a small gland inside the brain called the pituitary gland. The pituitary gland produces two different hormones, one called the follicle stimulating hormone ( FSH ) which is produced in increasing amounts in the first part of the cycle. This hormone stimulates the follicle to grow inside the ovary. As the follicle grows it produces in turn the female hormone called oestrogen( E2 ). During the course of your treatment we assess the satisfactory growth of the follicle by ultrasound scan to measure the size of the follicle in millimeters and blood tests to measure the oestrogen levels. The ultrasound scan cannot visualize the eggs. Hence we cannot assess the quality of the eggs. As the follicle reaches sufficient maturity and produces enough oestrogen hormone, the pituitary gland switches off the follicle stimulating hormone ( FSH ) and produces a quick burst of the second hormone called luteinizing hormone ( LH ) which ruptures the follicle releasing the egg 24 - 38 hours later. This time is the most fertile part of the menstrual cycle to achieve a pregnancy. There are kits available to check the presence of LH hormone in the early morning urine and thereby predict ovulation.

The ovarian follicle now starts to produce another hormone called the progesterone ( P4 ) just prior to its rupture in addition to oestrogen. The progesterone levels keep on increasing until the third part of the menstrual cycle. When you see your gynaecologist they often do a blood test on day 21 of the cycle to assess the level of progesterone to confirm the ovulation.

The ovarian oestrogen hormone acts on the uterus and starts developing the inner lining of the uterus called the endometrium. This is measured in its thickness by ultrasound scan during your treatment cycle. The progesterone hormone produced by the follicle after it has ruptured acts on the thickened endometrium and softens it so that if the fertilised egg ( embryo ) reaches the uterine cavity it can implant on the endometrium and grow as a pregnancy.

The free end of the fallopian tube with the help of finger-like projections called fimbriae picks up the egg that is liberated from the follicle in the ovary. The egg is then gradually propelled along the fallopian tube by very thin hair-like processes in the wall of the tube called cilia towards the uterus. The egg normally meets the sperm in the outer third of the fallopian tube. The sperm enters the egg and fertilises it. The fertilised egg now reaches the uterus in about four to five days and gets implanted on the endometrium already primed by the two ovarian hormones oestrogen and progesterone.

If the implantation occurs, the resulting early pregnancy produces a specific hormone called human chorionic gonadotophin ( hCG ). This is the hormone that is detected in your blood test on "day 14" of your treatment cycle if you are pregnant. The hCG hormone stimulates the now empty ovarian follicle ( corpus luteum ) from where the ovulation has taken place to produce more progesterone hormone. This progesterone helps the pregnancy to grow further. This cyclical hormone production will continue until the third month of pregnancy. By this time the placenta will produce enough oestrogen and progesterone hormone to sustain a pregnancy.

It is very important that your pregnancy is monitored for the first three months as nearly 30% of the pregnancies are lost in the first three months as miscarriage.

TO SUMMARISE, FOR A PREGNANCY TO OCCUR THE ESSENTIAL FACTORS ARE:

  • Release of an egg from one of the ovaries.
  • Congenial cervical mucus.
  • Open fallopian tube with good fimbriae and ciliae.
  • Adequately developed endometrial lining inside the uterine cavity.
  • Normal motile sperm to swim up from the vagina through the cervical mucus into the cervical canal, uterus and the fallopian tube.