INTERGROWTH-21st was a multicentre, multiethnic, population based project, conducted between 2009 and 2014 in eight countries.35 (link) The project’s primary aim was to study growth, health, nutrition, and neurodevelopment from less than 14 weeks’ gestation to 2 years of age, using the same conceptual framework as the World Health Organization Multicentre Growth Reference Study.36
The details of population selection have been described elsewhere.35 (link)
37 (link) In brief, all institutions providing obstetric care in eight urban areas in Brazil, China, India, Italy, Kenya, Oman, UK, and USA, with no or low levels of major, known, non-microbiological contamination, were chosen as study sites. From these populations, healthy women with a naturally conceived singleton pregnancy, and who met the individual inclusion criteria, were prospectively recruited into the Fetal Growth Longitudinal Study, one of the main components of the INTERGROWTH-21st Project.
Gestational age was estimated on the basis of the last menstrual period provided that the date was certain, the woman had a regular 24-32 day menstrual cycle, she was not using hormonal contraception or breastfeeding in the preceding two months, and the estimated gestational age (based on the last menstrual period) agreed (within seven days) with a standardised measurement of fetal crown rump length at 9+0 to 13+6 weeks’ gestation.30 (link)
38 (link)
39 (link) Follow-up visits occurred every five weeks (within one week either side)—that is, possible ranges were 14-18, 19-23, 24-28, 29-33, 34-38, and 39-42 weeks’ gestation.
At each visit, dedicated research staff who had undergone rigorous training and standardisation used the same protocols at all sites. Staff measured SFH first before taking fetal ultrasound measurements. With the woman in the supine position, having emptied her bladder, SFH was measured with a non-elastic metric tape (Chasmors) provided to all sites. After the start of the tape was positioned with one hand over the upper border of the symphysis pubis bone, the tape was placed in a straight line over the uterus until loss of resistance was felt when reaching the fundus. With the cubital edge of the hand used to sustain the tape in place at the point of the fundus, the tape was turned so that the numbers were visible to record the value to the nearest complete half centimetre.35 (link)
The process was then repeated to obtain a second measurement. Although it was not possible to blind the research staff to the gestational age at each visit, all SFH measurements were taken in a blinded fashion to reduce expected value bias by turning the tape measure so that no numbers were visible during the examination.
According to prespecified criteria, we excluded pregnancies complicated by fetal death or congenital abnormality, catastrophic or severe medical conditions (such as cancer or HIV); those with severe unanticipated conditions related to pregnancy that needed admission to hospital (such as eclampsia or severe pre-eclampsia); and those identified during the study who no longer fulfilled the entry criteria (such as women who started smoking during pregnancy or had an episode of malaria).
The details of population selection have been described elsewhere.35 (link)
37 (link) In brief, all institutions providing obstetric care in eight urban areas in Brazil, China, India, Italy, Kenya, Oman, UK, and USA, with no or low levels of major, known, non-microbiological contamination, were chosen as study sites. From these populations, healthy women with a naturally conceived singleton pregnancy, and who met the individual inclusion criteria, were prospectively recruited into the Fetal Growth Longitudinal Study, one of the main components of the INTERGROWTH-21st Project.
Gestational age was estimated on the basis of the last menstrual period provided that the date was certain, the woman had a regular 24-32 day menstrual cycle, she was not using hormonal contraception or breastfeeding in the preceding two months, and the estimated gestational age (based on the last menstrual period) agreed (within seven days) with a standardised measurement of fetal crown rump length at 9+0 to 13+6 weeks’ gestation.30 (link)
38 (link)
39 (link) Follow-up visits occurred every five weeks (within one week either side)—that is, possible ranges were 14-18, 19-23, 24-28, 29-33, 34-38, and 39-42 weeks’ gestation.
At each visit, dedicated research staff who had undergone rigorous training and standardisation used the same protocols at all sites. Staff measured SFH first before taking fetal ultrasound measurements. With the woman in the supine position, having emptied her bladder, SFH was measured with a non-elastic metric tape (Chasmors) provided to all sites. After the start of the tape was positioned with one hand over the upper border of the symphysis pubis bone, the tape was placed in a straight line over the uterus until loss of resistance was felt when reaching the fundus. With the cubital edge of the hand used to sustain the tape in place at the point of the fundus, the tape was turned so that the numbers were visible to record the value to the nearest complete half centimetre.35 (link)
The process was then repeated to obtain a second measurement. Although it was not possible to blind the research staff to the gestational age at each visit, all SFH measurements were taken in a blinded fashion to reduce expected value bias by turning the tape measure so that no numbers were visible during the examination.
According to prespecified criteria, we excluded pregnancies complicated by fetal death or congenital abnormality, catastrophic or severe medical conditions (such as cancer or HIV); those with severe unanticipated conditions related to pregnancy that needed admission to hospital (such as eclampsia or severe pre-eclampsia); and those identified during the study who no longer fulfilled the entry criteria (such as women who started smoking during pregnancy or had an episode of malaria).
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