… describes the merging of the female egg with the male sperm and the fusion of the male and female genomes. Unlike other cells, both gametes (female and male) contain only half a set of chromosomes (haploid). Combining the results in a complete set of chromosomes (diploid).
Fertilisation of the egg and sperm cells takes place in the fallopian tube. As soon as the gametes are merged, cell division begins. From now on, the developing baby is called an embryo. The embryo moves from the fallopian tube to the uterus. Further cell divisions take place as it makes its way there.
Definitive implantation in the uterine lining (endometrium) happens in the blastocyst stage. Implantation usually takes place on the 6th to 7th day after fertilisation.
The uterine lining must be optimally prepared for this. The hormone produced in the corpus luteum, progesterone, is the driver of these preparations. After successful implantation of the embryo, the hormone chorionic gonadotropin (hCG, human chorionic gonadotropin) starts to be released.
hCG is responsible for maintaining a pregnancy from the time of successful implantation. It also serves as proof of pregnancy as the hormone detected by commercially available rapid tests.
…fertile? The ability to become pregnant spontaneously, i.e. without supportive measures
…sub-fertile? Fertility is limited, but there are still significant chances of spontaneous pregnancy.
…infertile? The inability to maintain a pregnancy.
… sterile? The inability to get pregnant at all.
