What is the estimated date of delivery for a patient with a last menstrual period (LMP) date of [DATE] and no prior prenatal care?

Estimated Date of Delivery Calculation and Prenatal Care Recommendations

Calculating the Estimated Date of Delivery

To calculate the estimated date of delivery (EDD), add 280 days (40 weeks) to the first day of the last menstrual period, which is the standard method known as Naegele's rule. 1

• Gestational age is calculated from the first day of the last menstrual period (LMP), with pregnancy duration typically 280-290 days from this date 1, 2
• The EDD is reported as the date when the patient reaches 40 weeks and 0 days of gestation 1
• For example, if LMP was January 1st, the EDD would be October 8th (adding 280 days) 3

Confirming Accuracy of Dating

Since this patient has had no prenatal care, ultrasound dating should be obtained as soon as possible to confirm or adjust the EDD based on LMP. 4

• Ultrasound examination in the second trimester (17-22 weeks) is the most accurate predictor of delivery date at the individual level, followed by first-trimester ultrasound 4
• First-trimester ultrasound using crown-rump length measurement should be performed if the patient presents early enough (before 14 weeks) 1
• If there is a discrepancy between LMP dating and ultrasound dating, ultrasound measurements should guide the final EDD, particularly when obtained in the first or early second trimester 4

Essential Prenatal Education for Patients Without Prior Care

Immediate Clinical Actions Required

This patient requires urgent establishment of prenatal care with comprehensive initial assessment including dating ultrasound, routine prenatal laboratory testing, and risk stratification. 1

• Confirm pregnancy with serum hCG if not already done (hCG >5 mIU/mL indicates pregnancy) 1
• Obtain dating ultrasound to confirm gestational age, number of fetuses, cardiac activity, and pregnancy location 1
• First-trimester ultrasound should visualize gestational sac (visible at 5 weeks), yolk sac (visible at 5.5 weeks), and embryo with cardiac activity (visible at 6 weeks on transvaginal ultrasound) 1

Critical Timing Information

Educate the patient that the first trimester extends through 13 weeks 6 days of gestation, and certain time-sensitive interventions and screenings must occur within specific gestational age windows. 1

• First-trimester screening for aneuploidy should be performed between 11-14 weeks if desired 1
• Anatomy ultrasound is typically performed at 18-22 weeks gestation 1
• The patient should understand that term pregnancy is defined as 37 weeks 0 days through 41 weeks 6 days 1, 2

Warning Signs Requiring Immediate Evaluation

Instruct the patient to seek immediate care for vaginal bleeding, severe abdominal pain, decreased fetal movement (once movement is established), fever, or signs of preterm labor. 1

• Vaginal bleeding in early pregnancy may indicate miscarriage, ectopic pregnancy, or other complications requiring urgent evaluation 1
• Miscarriage is defined as spontaneous loss of intrauterine pregnancy prior to 20 completed weeks of gestational age 1
• Stillbirth is defined as fetal death after 20 completed weeks of gestational age 1

Medication and Lifestyle Counseling

Advise immediate initiation of prenatal vitamins with folic acid (400-800 mcg daily), avoidance of alcohol and tobacco, and discussion of any current medications for safety in pregnancy. 1

• Certain medications are contraindicated in pregnancy and require immediate discontinuation or substitution 1
• Chemotherapy should not be administered during the first trimester due to high risk of fetal congenital malformations reaching 20% 1