Accurately Dating Pregnancy
Nagele's Rule involves subtracting three months, adding one week and one year to the first day of the last menstrual period (LMP). Thus, if a woman's LMP was December 1, 2003, one would arrive at September 8, 2004, as an estimated date of delivery (EDD).
In spite of the fact the Nagele's Rule seems to misrepresent the mean length of gestation by a few days, the calculation of an EDD by this method, which is based upon a good menstrual history, is reasonably accurate. Spontaneous delivery will take place in approximately 90 percent of all gravid women by the end of the 41st week of pregnancy.
Women should be widely educated about the importance of recording their menstrual periods. Registration for prenatal care within the first six weeks of pregnancy should become standard practice. Menstrual history should be recorded carefully and completely on the first prenatal visit. If the uterus is too small to size on the first prenatal visit, the next visit can simply be scheduled at the usual interval, allowing the physical findings of the bimanual examination to contribute to the data base at the time. The practice of encouraging women to wait for several weeks to pass before prenatal care is initiated is counterproductive to a good history and contradicts what research has shown about the value of early prenatal care.
A "due date" should be presented as the midpoint in a four-week range. Women should be advised that prior gestational length that has not been affected by external factors may be a guide as to expectations for a current pregnancy. When insufficient information exists to make a reasonable judgment about gestational age at the time of a prenatal visit, the practitioner needs to make this clear. collecting historical data prepares the patient for further investigation, whether that is assessed data confirmation or ordering laboratory work, or a request for an ultrasound examination.
Current pregnancy History
History of the current pregnancy include the following
Pregnancy history to date-support network, coping and stress levels experienced since last visit, nutritional intake/changes, behavioral changes regarding smoking, alcohol, substance abuse and exercise, any common discomforts.
Any problems or danger signs which have occurred since the last visit such as vaginal bleeding, infections (e.g., UTI), uterine contractions, or pelvic inflammatory disease (P.I.D.) signs and symptoms.
Confirmation that the client understands any recommendations made or treatments provided.
Ask the client to ascertain what normal and abnormal signs and symptoms of pregnancy she has experienced; inquire about the dates of the last menstrual period and the last normal menstrual period, and compute the estimated date of conception. Determine the weeks of gestation at the present time.
In addition to menstrual data and sonographic biometry, other information obtained from the patient's history can be important in determining gestational age. Basal body temperature data and other ovulatory history data must be considered and used to determine gestational age when available. Correction for a prolonged intermenstrual interval should be considered for determining the post-term gestation. History taking should also screen for factors that may cause delayed ovulation, such as irregular menses, ovulation-inducing agents, and recent discontinuance of oral contraceptive agents. Secondary to menstrual data, the fundus reaching the umbilicus at 20 weeks was the second most sensitive indicator of gestational age. Other parameters of measured fundal height, quickening, and first auscultated fetal heart tones were found to have equal accuracy. First-trimester examination of the pregnant uterus is usually helpful for verification of gestational age except in the obese patient or in the patient with uterine malformations..