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Ages Eligible for Study:
21 Years and older (Adult, Senior)
Sexes Eligible for Study:
Accepts Healthy Volunteers:
21 years of age or older
second pregnancy, singleton
conceived without fertility treatments
Preexisting medical conditions
Sexually transmitted diseases
Medical complications during pregnancy
Medications during pregnancy known to influence fetal growth
Smoking, alcohol drinking
Excessive physical activity level which could affect the outcome of interest.