Fertilization Process
A pregnancy is the result of a very complex process involving the
female and
male's reproductive organs and their respective
regulatory mechanisms. In order for a couple to conceive, 4 basic
requirements must be met:
- Normal semen sample.
- Normal oocytes (eggs).
- Normal female reproductive pathway.
- Correct environment for implantation of the embryo.
At midcycle (± day 14) ovulation occurs under hormonal control,
whereby the mature (dominant) follicle ruptures releasing the oocyte.
The oocyte is retrieved by the fimbriae (finger-like structures) of
the Fallopian tube and slowly transported down the tube.
Sexual intercourse must occur within a certain time period before
or after ovulation, as the oocyte's capacity to be fertilized is
time dependent (± 24 hours after ovulation). During sexual
intercourse semen is deposited in the upper section of the vagina.
From the semen deposited, sperm migrate through the cervical mucus
into the uterus. (Sperm may survive in the reproductive pathways
for more than 72 hours) During their progress through the uterus
into the fallopian tube the sperm undergo changes to enable them
to engage an oocyte. Upon reaching the oocyte the sperm undergoes
further physical changes that allow it to pass through its cellular
(cumulus cells) and a cellular (zona pellucida) envelopes. The sperm
attaches itself to the oocyte and passes into the oocyte. At the
moment of penetration the oocyte undergoes changes preventing a
second sperm from entering.
The formation of a male and female pronucleus signals a successful
fertilization (union of the male and female gametes). During its
further progress down the Fallopian tube an embryo develops. The
embryo enters the uterus 3-4 days after ovulation.
The developing embryo implants itself into the endometrium (uterus
lining) approximately 8 days after ovulation and develops into a
normal conceptus.
A blood hormone determination performed 12 days after ovulation
can be used as a sign of successful implantation. Urine tests can
indicate a possible pregnancy, if the following menstruation is
missed.
The confirmation of a normal conception is performed 7 to 8 weeks
after the first day of the last menstruation by means of ultrasound.
The presence of a viable pregnancy is confirmed by the identification
of the fetal sac and the visualisation of the fetal heart beat.
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