Obstetric ultrasound dating and lmp

Due Date Calculator

obstetric ultrasound dating and lmp

The estimated date of delivery (EDD) pregnancy calculator equation Gestational Age by LMP is calculated from the first day of the last menstrual period. Keywords: ultrasound dating, prolonged pregnancy, Nigeria the last menstrual period (LMP) and a prediction from obstetric ultrasound scan. You can calculate your due date by subtracting three months from the first day of your last menstrual period (LMP) and then add a week. Use our pregnancy.

Morin L, Lim K. Ultrasound in twin pregnancies. J Obstet Gynaecol Can. Sperling L, Tabor A. Acta Obstet Gynecol Scand. Method for estimating due date. Ameri-can College of Obstetricians and Gynecologists.

obstetric ultrasound dating and lmp

The timing of the "fertile window" in the menstrual cycle: Timing of sexual intercourse in relation to ovulation. Effects on the probability of conception, survival of the pregnancy, and sex of the baby.

Determination of Gestational Age by Ultrasound No. J Obstet Gynaecol Can ;36 2: Martin JA, et al. Natl Vital Stat Rep. Page JM, The risk of stillbirth and infant death by each additional week of expectant management in twin pregnancies.

Epub Mar Risk of late-preterm stillbirth and neonatal morbidity for monochorionic and dichorionic twins. Epub Mar 5. The commonest indication for induction of labor in the two hospitals and in our environment is prolonged pregnancy. Every singleton pregnant woman due for a routine delivery planning discussion at a gestational age of 36 weeks and beyond was eligible for the study.

Exclusion criteria included uncertainty of date, presence of contraindications to vaginal delivery, irregular menstrual cycle prepregnancy, use of hormonal contraceptives prior to pregnancy, or bleeding during pregnancy.

After individual counseling of eligible participants, pretested structured questionnaires were administered to consecutive consenting women by trained medical interns. Ethical clearance for the study was obtained from the institutional review board of the University of Nigeria Teaching Hospital, Enugu. Data collected included the sociodemographic characteristics of the respondents age, marital status, tribe, level of education, occupation, parityopinions and preferences regarding LMP and ultrasound scan dates, and their attitudes toward postdatism and induction of labor in relation to estimated dates.

The primary outcome measure was willingness to accept induction of labor at an LMP-derived gestational age of 40 weeks plus 10 days when late pregnancy ultrasound scan-derived gestational age was less than 40 weeks plus 10 days. The first trimester was defined as a gestational age of 1—13 weeks, the second trimester as 14—27 weeks, and the third trimester as 28—42 weeks.

Further, the early second trimester was defined as a gestational age of 15—22 weeks and the late second trimester as 23—27 weeks. Frequency tables were generated for relevant variables. A P-value of less than 0.

Women's Health Care Physicians

Results A total of questionnaires were administered, but only were completed correctly, giving a response rate of Accordingly, in creating recommendations and the associated summary table, single-point cutoffs were chosen based on expert review.

Because this practice assumes a regular menstrual cycle of 28 days, with ovulation occurring on the 14th day after the beginning of the menstrual cycle, this practice does not account for inaccurate recall of the LMP, irregularities in cycle length, or variability in the timing of ovulation. It has been reported that approximately one half of women accurately recall their LMP 2—4.

Accurate determination of gestational age can positively affect pregnancy outcomes.

obstetric ultrasound dating and lmp

For instance, one study found a reduction in the need for postterm inductions in a group of women randomized to receive routine first-trimester ultrasonography compared with women who received only second-trimester ultrasonography 5. A Cochrane review concluded that ultrasonography can reduce the need for postterm induction and lead to earlier detection of multiple gestations 6. Because decisions to change the EDD significantly affect pregnancy management, their implications should be discussed with patients and recorded in the medical record.

Pregnancy Dating

Measurements of the CRL are more accurate the earlier in the first trimester that ultrasonography is performed 11, 15— The measurement used for dating should be the mean of three discrete CRL measurements when possible and should be obtained in a true midsagittal plane, with the genital tubercle and fetal spine longitudinally in view and the maximum length from cranium to caudal rump measured as a straight line 8, Mean sac diameter measurements are not recommended for estimating the due date.

Dating changes for smaller discrepancies are appropriate based on how early in the first trimester the ultrasound examination was performed and clinical assessment of the reliability of the LMP date Table 1. For example, for a day-5 embryo, the EDD would be days from the embryo replacement date. Likewise, the EDD for a day-3 embryo would be days from the embryo replacement date. Clinical Considerations in the Second Trimester Using a single ultrasound examination in the second trimester to assist in determining the gestational age enables simultaneous fetal anatomic evaluation.

obstetric ultrasound dating and lmp

With rare exception, if a first-trimester ultrasound examination was performed, especially one consistent with LMP dating, gestational age should not be adjusted based on a second-trimester ultrasound examination. Ultrasonography dating in the second trimester typically is based on regression formulas that incorporate variables such as the biparietal diameter and head circumference measured in transverse section of the head at the level of the thalami and cavum septi pellucidi; the cerebellar hemispheres should not be visible in this scanning plane the femur length measured with full length of the bone perpendicular to the ultrasound beam, excluding the distal femoral epiphysis the abdominal circumference measured in symmetrical, transverse round section at the skin line, with visualization of the vertebrae and in a plane with visualization of the stomach, umbilical vein, and portal sinus 8 Other biometric variables, such as additional long bones and the transverse cerebellar diameter, also can play a role.

Date changes for smaller discrepancies 10—14 days are appropriate based on how early in this second-trimester range the ultrasound examination was performed and on clinician assessment of LMP reliability. Because of the risk of redating a small fetus that may be growth restricted, management decisions based on third-trimester ultrasonography alone are especially problematic; therefore, decisions need to be guided by careful consideration of the entire clinical picture and may require close surveillance, including repeat ultrasonography, to ensure appropriate interval growth.

The best available data support adjusting the EDD of a pregnancy if the first ultrasonography in the pregnancy is performed in the third trimester and suggests a discrepancy in gestational dating of more than 21 days. Conclusion Accurate dating of pregnancy is important to improve outcomes and is a research and public health imperative.

Methods for Estimating the Due Date - ACOG

As soon as data from the LMP, the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record. The American College of Obstetricians and Gynecologists, the American Institute of Ultrasound in Medicine, and the Society for Maternal—Fetal Medicine recognize the advantages of a single dating paradigm being used within and between institutions that provide obstetric care.

Table 1 provides guidelines for estimating the due date based on ultrasonography and the LMP in pregnancy, and provides single-point cutoffs and ranges based on available evidence and expert opinion. Fetal Imaging Workshop Invited Participants.