Your last period will be the most recent period you had before finding out you’re pregnant. The first day of that period represents the first day of your cycle.  The date of your last period is typically used instead of your conception date because most women do not know their conception date. Conception can occur 11-21 days after the first day of your last period, and sperm can survive in the body for a few days after intercourse to fertilize an egg. Your baby will be due 280 days after the first day of your last period, which works out to forty weeks. This also represents ten lunar months, or 28-day cycles. Typical pregnancies last about 37-38 weeks but are estimated at 40 since conception usually occurs about two weeks after the date of your last period, which is the date used to estimate the due date. You can also calculate your due date by counting back three months from the first day of your last period, adding seven days, and then adding a year. This will provide you with an estimated due date.  Naegele's rule provides an alternative for calculating your due date that's easier for some people to do in their head. For example, if your last period began on August 8, then you could count back three months to May 8. If you add seven days, you'd get May 15. Your due date would then be next May 15. Using the date of your last period works best for 28-day cycles. If you have an irregular cycle, you may need to wait until your medical provider can perform an ultrasound to get an estimated due date.

How would you rephrase that briefly using Indonesian?
Tentukan tanggal hari pertama haid terakhir. Hitung 40 minggu dari tanggal haid terakhir. Gunakan aturan Naegele sebagai alternatif. Sampaikan kepada dokter jika haid Anda tidak teratur.