When should I take a pregnancy test?
If you're using an at-home urine test, the results are the most accurate about 1 to 7 days after missing your period, although it's possible to test positive before then. This is because in order for pregnancy to occur, a few important steps must come first: ovulation, fertilization, and a few days later, implantation of the blastocyst. A blastocyst is a fertilized egg, and its implantation into the uterine wall prevents you from having a period.
Pregnancy tests measure a hormone called beta-human chorionic gonadotropin, or beta-hCG, which doesn't appear until after implantation. This is why testing too early is more likely to result in a false negative. A false negative means the test incorrectly indicates that you're not pregnant, even though you are. During the first trimester, beta-hCG increases drastically, meaning the more time after conception, the more likely you are to see a positive result.
How do I calculate hCG levels from my last period?
hCG levels rise during pregnancy and can be estimated based on how many weeks have passed since the first day of your last menstrual period (LMP). Pregnancy is typically measured from LMP, with hCG levels rising rapidly in early weeks.
Since hCG levels vary widely, only a blood test can provide an exact measurement. If you’re tracking hCG for pregnancy confirmation or concerns, consult your healthcare provider.
How does a pregnancy due date calculator work?
A pregnancy due date calculator estimates the date your baby is likely to be born, or estimated date of delivery (EDD), based on information about your menstrual cycle or conception date. Here's how it typically works:
1. Based on the First Day of Your Last Menstrual Period (LMP)
This is the most common method and assumes a 28-day menstrual cycle with ovulation on day 14:
- It adds 280 days (or 40 weeks) to the first day of your last period.
- This includes the two weeks before ovulation, even though conception hasn’t happened yet—because pregnancy is counted from the start of your last period, not from the day you actually conceived.
2. Based on Conception Date (if known)
If you know the exact day you conceived (through fertility tracking, IUI, IVF, etc.), you can add 266 days (or 38 weeks) to that date to estimate your due date.
3. Adjustments for Irregular Cycles
This calculator lets you enter your average cycle length. If your cycle is longer or shorter than 28 days, the calculator adjusts accordingly:
- For a 35-day cycle, ovulation may happen around day 21 rather than day 14, so your due date shifts later.
4. Ultrasound-Based Estimations
Especially in early pregnancy, ultrasounds can provide a more accurate due date than LMP—especially if your cycle is irregular or if you’re unsure of your dates. This estimation can be done by your provider.
How does the IVF due date calculator work?
To calculate your pregnancy due date for a fresh in vitro fertilization (IVF) transfer, 266 days are added to the date of egg retrieval or fertilization. For a frozen embryo transfer, the calculation depends on the embryo's stage at the time of transfer:
- If a day-3 embryo is used, the due date is 263 days from the transfer date
- If a day-5 blastocyst is used, the due date is 261 days from the transfer date
What is gestational age?
Gestational age refers to the length of pregnancy, measured in weeks, from the first day of the last menstrual period (LMP) to the current date. It is the standard way to track pregnancy progression and estimate due dates. This method, however, cannot account for misremembering the exact LMP, nor irregularities in ovulation and menstruation, so additional methods, like ultrasounds, are also used to calculate gestational age.
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