Question

Consider the normal path of an ovum as it leaves the ovary and enters the uterine tube.

If ovulation occurs at day 14 of a 28-day cycle, but a woman has conception on day 19 (so conception has occurred in the uterus), what do you think would be the likely series of events to follow?
Would implantation occur?
If it does, what might be the problems, or is it a normal implantation?
Can she have a "tubal" pregnancy?

Answer 1

Menstrual cycle in female has four phases. In the ovulation phase, the release of the ovum or secondary oocyte takes place by the rupture of mature graafian follicle from either one of the ovary under the influence of high luteinizing hormone in the body. The secondary oocyte will be released into the pelvic cavity, captured and sweeped inside the fallopian tube by the finger like structure of fallopian tubes known as fimbriae. Once the secondary oocyte enter into the uterine tube, it travels to infundibulum and then further move to the ampule of the uterine tube and stays there. The life span of the ovum is 12-24 hours following the release.

If the ovum is not fertilized within 24 hours of its life span, it will degenerate and breakdown due to decrease in level of luteinizing hormone.

As per the given question, if the ovulation occur on 14 th day of a menstrual cycle, the ovum will be alive till 16 th day and degenerate if not fertilized. The fertilization always occur in the ampule of the fallopian tube, the ovum will not move to uterus for fertilization.

If the ovum is fertilized with the sperm, it travels 3- 4 days through the uterine tube and then finally move to the uterine cavity for implantation in day 6 following fertilization.

Events following fertilization.

Day 1: fertilization occur within the ampulla of the fallopian tube within 24 hours of ovulation. The egg start to move towards uterus.

Day 2 : the fertilized egg become zygote by single division,the number of cells become two followed by second mitotic division and the cell number become four.

Day 3 and 4 : Rapid mitotic cell division occur and the zygote become a sphere like structure called morula.

Day 5 : The morula undergo further division and become a 16 cell structure blastocyst. It enter into the uterine cavity.

Day 6: The implantation of blastocyst to the uterine endometrial lining takes place.

So if the fertilization happened on 14 th day of menstrual cycle in the fallopian tube, the implantation occur on the 20 th day in the uterus.

Tubal pregnancy is also known as ectopic pregnancy which occur when the fertilized ovum get stuck in the uterine tube. The reason are abnormal anatomy of uterine tube, hormonal imbalances, any infection, inflammation or damage to the uterine tube and abnormal development of fertilized egg.