Gestational age

Examples of Gestational age in the following topics:

• Inference for linear regression

  • The estimated regression line is $\hat{headcircumference}$ = 3.91 + 0.78×gestational age
  • (a) What is the predicted head circumference for a baby whose gestational age is 28 weeks?
  • (b) The standard error for the coefficient of gestational age is 0.35, which is associated with df = 23.
  • Does the model provide strong evidence that gestational age is significantly associated with head circumference?
  • There is an association between gestational age and head circumference.

• Fifth Through Eighth Weeks of Development

  • Gestational age is the time that has passed since the onset of the last menstruation, which occurs two weeks before the actual fertilization.
  • Embryonic age measures the actual age of the embryo or fetus from the time of fertilization.
  • Thus, the first week of embryonic age is already week three counting with gestational age.
  • By week eight of gestation, the embryo measures 13 millimeters in length.
  • The features are consistent with a developmental age of seven weeks (the ninth week of menstrual age).

• Metabolic Changes

  • Maternal insulin resistance can lead to gestational diabetes.
  • Gestational diabetes (or gestational diabetes mellitus, GDM) is a condition in which women without previously diagnosed diabetes exhibit high blood glucose levels during pregnancy (especially during the third trimester).
  • Gestational diabetes is caused when the insulin receptors do not function properly.
  • Gestational diabetes generally has few symptoms and it is most commonly diagnosed by screening during pregnancy.
  • Babies born to mothers with untreated gestational diabetes are typically at increased risk of problems such as being large for gestational age (which may lead to delivery complications), low blood sugar, and jaundice.

• Development of the Extraembryonic Coelom

  • An artificially colored image of the contents in the cavity of the uterus seen at approximately 5 weeks of gestational age by obstetric ultrasonography.

• Prenatal Diagnostic Tests

  • ., amniocentesis (that can be done from about 14 weeks gestation up to about 20 weeks), and chorionic villus sampling (that can be done earlier: between 9.5 and 12.5 weeks gestation).
  • The American Congress of Obstetricians and Gynecologists guidelines currently recommend that all pregnant women, regardless of age, be offered invasive testing to obtain a definitive diagnosis of certain birth defects.
  • At about 6 weeks of pregnancy, an ultrasound dating scan may be offered to help confirm the gestational age of the embryo and check if a single or twin pregnancy exists, but such a scan is unable to detect common abnormalities.
  • The results of the blood tests are then combined with the NT ultrasound measurements, maternal age, and gestational age of the fetus to yield a risk score for Down syndrome, trisomy 18, and trisomy 13.

• Abortion

  • Early medical abortions account for the majority of abortions before 9 weeks gestation in Britain, France, Switzerland, and the Nordic countries.
  • Up to 15 weeks' gestation, suction-aspiration or vacuum aspiration are the most common surgical methods of induced abortion.
  • From the 15th week of gestation until approximately the 26th, other techniques must be used.
  • The risk of abortion-related mortality increases with gestational age, but remains lower than that of childbirth through at least 21 weeks' gestation.
  • The use of abortion procedures is dictated primarily by gestational time period.

• Multiple and logistic regression solutions

  • 8.3: (a) baby weight = −80.41 + 0.44 × gestation − 3.33 × parity − 0.01 × age + 1.15 × height + 0.05 × weight − 8.40 × smoke.
  • (b) β gestation : The model predicts a 0.44 ounce increase in the birth weight of the baby for each additional day of pregnancy, all else held con$R^2_{adj}$stant.β age : The model predicts a 0.01 ounce decrease in the birth weight of the baby for each additional year in mother's age, all else held constant.
  • 8.7: (a) There is not a significant relationship between the age of the mother.We should consider removing this variable from the model.
  • However, since the adjusted R2 for the model with gestation is higher, it would be preferable to add gestation in the first step of the forward-selection algorithm.
  • The residuals vs.length of gestation plot also does not show any clear or strong remaining structures, with the possible exception of very short or long gestations.

• Introduction to Pregnancy and Human Development

  • Pregnancy is the period of gestation from the fertilization of an egg, through development of a fetus, and ending at birth.
  • The term embryo is used primarily for developing humans up to eight weeks after fertilization (to the 10th week of gestation).
  • In a pregnancy, there can be multiple gestations, as in the case of twins or triplets.
  • Ultrasound is used to monitor the age and health of the fetus during pregnancy.

• Early Pregnancy Tests

  • With obstetric ultrasonography the gestational sac sometimes can be visualized as early as four and a half weeks of gestation (approximately two and a half weeks after ovulation) and the yolk sac at about five weeks' gestation.
  • The heartbeat may be seen as early as six weeks, and is usually visible by seven weeks' gestation.
  • Inaccurate estimations of fetal age and inaccuracies inherent in ultrasonic examination may cause a scan to be interpreted negatively.

• Model selection exercises

  • (b) The summary table below shows the results of the model with the age variable removed.
  • 8.7: (a) There is not a significant relationship between the age of the mother.
  • 8.9: Based on the p-value alone, either gestation or smoke should be added to the model first.
  • However, since the adjusted R2 for the model with gestation is higher, it would be preferable to add gestation in the first step of the forward-selection algorithm.