The estimated due date is calculated by adding 280 days to the first day of your last period. However, the duration of pregnancy is influenced by the age of the mother, the time of implantation of the embryo, the weight of the mother herself at the time of birth. It was found that with every year of her life, a woman bears a child for 1 day longer. And for every “extra” 100 grams of weight at birth, we also add 1 day to the duration of pregnancy. During the study, it was also found that embryos require different times for implantation (fixation in the uterus). And those embryos that took longer to implant also require more time from implantation to birth. More precisely, the date of birth can be determined using ultrasound.