![]() This means (Corrected) LMP = Date of egg collection minus 14. This is your "corrected LMP" (last menstrual period). Just subtract 14 from your date of ovulation. Since every IVF patient knows the date they ovulated (= the day of egg collection), it's easy to calculate your menstrual age. This is because we can use this landmark for all situations (including IUI pregnancies for Day 3 embryo transfers and Day 5 embryo transfers and frozen cycles as well !) The key reproductive event you need to focus on is ovulation! It makes much more sense to talk about the pregnancy in terms of DPO (days post ovulation), rather than the menstrual age or the day of the embryo transfer. So how do you convert the date of your embryo transfer to menstrual age? This is surprisingly simple. This means that even though you are actually being more scientifically accurate, you will have to follow the norms which clinicians use. The trouble is that if you calculate your gestational age from the date of the embryo transfer or the date of fertilization, your obstetrician will get confused, because he is used to calculating the age of the pregnancy in menstrual weeks – not the embryonic age. When you do IVF, you do not need to use the date of your last menstrual period to calculate your due date – you have far more information, which is much more biologically reliable. However, since the vast majority of women know their menstrual cycle well, it’s easy and convenient to use menstrual age for dating the pregnancy in clinical practice, in order to simplify matters. The reason for this is that most women don’t know on which date they ovulated or on which day they had sex, which led them to get pregnant. ![]() ![]() This means on 1 Feb, while the embryo’s age is only 4 weeks, the doctor will say she is 4 weeks pregnant! This is a clinical norm we use, which refers to the menstrual age, and not the actual age of the fetus. However, the baby was probably conceived around January 14. Therefore, if a woman with a 28-day cycle had her last period on January 1, her due date is 8 October. Now we know that a woman cannot get pregnant before she ovulates – and ovulation, fertilization and conception occur about 14 days from the start of the menstrual cycle. This is an estimate, calculated from the first date of the last menstrual period. ![]() Your due date is usually calculated based on a 40 week average gestational age. Too much data can confuse the poor patient, because you just want to know when your bundle of joy will be with you. Doctors often make matter worse, especially when they do hCG tests and ultrasound scans. One would think that creating an IVF pregnancy calculator should be much easier, because we know the exact date on which the eggs were retrieved and the embryos were transferred! However, it can be more confusing, because of the difference between menstrual age and embryonic age. The principle is quite simple – they just need to key in their LMP (first day of their last menstrual period) and the calculator will tell them their due date (by adding 40 weeks do the LMP, a rule of thumb called Naegle’s rule). There are lots of pregnancy calculators online, which allow women to calculate their due date. The moment you find out you are pregnant, the next question is – when is my baby due? This is true, whether you get pregnant in your bedroom, or after doing IVF! ![]()
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