Normal cycle
During each menstrual cycle, a woman's ovaries release an egg. This process is called ovulation. The follicle develops into a corpus luteum, which can produce and release estrogen and progesterone for a specific period, i.e., 12-14 days only if the woman is not pregnant. To continue to produce these hormones, the corpus luteum needs to be triggered by another hormone called "human chorionic gonadotropin" (HCG).
This hormone is produced by the placenta from the time of embryo implantation. Therefore, if the woman is not pregnant, the corpus luteum will stop producing the hormones 12-14 days after ovulation, and menstruation will follow. This phenomenon is called "program cell death" or "apoptosis".
Consequently, ovulation can be calculated or estimated very easily by deducting 14 days from the time of menstruation. Thus, in a 28-day normal ovulatory cycle, day of ovulation would be day 14. If the cycle length is 30 days, the day of ovulation would be calculated as day 16.
Duration of pregnancy is calculated from the first day of the menstrual cycle and its period is around 40 weeks; 280 days (266 days to the day of ovulation) i.e. 14 days from day 1 of the menstrual cycle.
Therefore, to calculate the theoretical day of the last menstrual period (LMP), in order to calculate the duration of pregnancy in patients who are being treated for ovulation induction, no matter what treatment the patient is undergoing, the calculation would need to be as follows:
Ovulation time: The theoretical LMP can be considered as:
Reduction of 14 days (2 weeks) to the day of ovulation
Following insemination: The theoretical LMP can be considered as:Reduction of 14 days (2 weeks) to the day of insemination;
IVF: The theoretical LMP can be considered as:Reduction of 14 days (2 weeks) to the day of egg collection
Replacement of frozen-thawed embryo (3 days): The theoretical LMP can be considered as:
Reduction of 17 days to the day of embryo replacement
Replacement of frozen-thawed embryo (blastocyst): The theoretical LMP can be considered as:
Reduction of 19 days to the day of embryo replacement
Therefore, if IVF treatment is performed using various drugs for pituitary desensitization and stimulation, in fact the practical length of the cycle during the stimulation until the time of egg collection does not have any influence on the duration of the pregnancy. This period will always be considered to be 14 days.
If you wish to use a calculator for these purposes you can log into:
For natural cycle
http://www.ivf.ca/naturalpregduedate.php
For IVF cycles
http://www.ivf.ca/duedatecalculators.htm
Due day of delivery:
For delivery information only -However, only 5% of pregnant women delivered on the specific due day. Most delivered 2 weeks before or after this day.
