Research suggests that the most accurate time for an ultrasound is between 11-14 weeks gestational age (9). Ultrasounds, also called sonograms or sonos, can be more accurate than LMP at predicting the date of birth if performed early in pregnancy (9). This is because of two reasons: estimating gestational age is a varied and complicated process and pregnancies naturally vary from person to person and pregnancy-to-pregnancy (1). Ultrasound can more accurately predict the estimated due dateĪbout 4-5% of women and pregnant people birth on their estimated due date (1, 8, 9). Women and people who are breastfeeding/chest feeding can ovulate before their period has returned Time between fertilization and implantation varies Time from conception to fertilization varies This can cause ovulation to occur earlier or later than day 14 of the cycle The length of the follicular phase of the cycle can vary. Recent hormonal contraceptive use can impact both bleeding and ovulation
Calculate due date full#
Many factors make this method less than perfect, like cycle length and ovulation date variations (3-7):Ī person may not know their last period start date (tracking your first full flow day with the Clue app makes sure that you do)Įarly pregnancy bleeding can look like a period When an estimated due date is based on your last period, it assumes that you have 28-day cycles and that you ovulated on day 14 (1). A due date based on the last menstrual period doesn’t work for everyoneīecause every body is different, and each cycle is unique, an estimated due date based on the last menstrual period won’t be accurate most of the time, unless you have a scheduled labor induction or cesarean section. The period is the time when the ovaries are the most inactive as your body prepares for all the hormonal changes of the upcoming cycle (2). It starts with the first day of your period, your LMP. The first phase of the menstrual cycle is called the follicular phase (3).
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