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Diagnosis and outcome of first-trimester growth delay

Joan M Mastrobattista, MD
Deborah Levine, MD
Section Editor
Lynn L Simpson, MD
Deputy Editor
Vanessa A Barss, MD, FACOG


Prior to the widespread use of ultrasound in early pregnancy, first-trimester growth was thought to be uniform and under genetic control. Differences in fetal growth rates were not believed to manifest until the second half of pregnancy. However, these beliefs were challenged after analysis of data from thousands of first-trimester ultrasound examinations [1-5]. Early delay in fetal growth has been documented in pregnancies with precise gestational age dating, and appears to be predictive of subsequent adverse perinatal outcomes, such as fetal aneuploidy, growth restriction, and preterm birth. These perinatal outcomes can affect health and disease risks later in life.

In this discussion, the term "fetus" will be used regardless of gestational age, even though "embryo" is the biological term for early human life (ie, implantation through eight weeks postconception) and "fetus" is the biological term for human intrauterine life thereafter.


The diagnosis of growth delay is based upon fetal size that is smaller than expected based on last menstrual period (LMP),early sonographic dating, or timing of embryo transfer in pregnancies resulting from assisted reproductive technology (table 1). Thus, it is crucial to have accurate information on the fetus' gestational age and the normal size range for fetuses of that age.

Pitfalls in determining gestational age

Use of last menstrual period — When clinicians date a pregnancy based on menstrual weeks (menstrual age), the first trimester of pregnancy is defined as the time interval beginning on the first day of the LMP and ending 13 weeks later. However, this calculation can lead to errors in assessment of gestational age and, in turn, estimated delivery date (EDD) because:

Many women do not have regular 28-day cycles and thus do not ovulate (or conceive) on day 14 of the cycle. The difference between the observed and expected size of embryos/fetuses is thus biased towards smaller than expected measurements since the timing of ovulation is skewed to the second half of the cycle.

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Literature review current through: Nov 2017. | This topic last updated: Aug 07, 2017.
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