The goal of this study is to learn how being exposed to high environmental temperatures during pregnancy affects the health of pregnant women and their babies. The study also aims to understand how the body responds to heat stress during pregnancy and how this might lead to pregnancy complications and birth problems like early birth or low birth weight.
The main questions that the study aims to answer are:
1. What are the acute and chronic effects of environmental heat exposure on pregnancy and birth outcomes across different trimesters? 2. Through which biological pathways does heat stress impact maternal, fetal, and infant health across varying gestational ages? 3. How do socio-demographic factors, maternal characteristics, and nutritional status of women modify the relationship between environmental heat exposure and adverse pregnancy outcomes?
The study will take place in rural parts of Sindh, Pakistan. These areas often experience extreme heat and have limited access to electricity or cooling systems like fans or air conditioners.
This study will include pregnant women who are in their first trimester (under 14 weeks of pregnancy). Before starting any study activities, researchers will explain the study to each woman in a language she understands and ask for her written permission to take part (informed consent).
At the beginning of the study, participants will visit a study clinic. During this visit, researchers will check their height and weight, perform an ultrasound, and collect a small amount of blood for testing. Participants will also be asked to wear a small device that measures the air temperature and humidity in their surroundings.
The researchers will follow each participant during her pregnancy, with visits during the second and third trimesters at the study clinic. At each visit, researchers will check how much heat the participant has been exposed to using the data from the device and from her own answers to a simple questionnaire. The questionnaire will have questions about their heat exposure at work, home, type of clothing, and how they deal with hot weather. Serial ultrasound, blood and urine tests will be conducted so researchers can study signs of stress, hydration, and other changes in the body. A smaller group of participants will also wear a device to measure their body skin temperature, heart rate, physical activity and sleep during pregnancy.
When the baby is born, researchers will collect information about the birth, including the baby's weight and length, the time of delivery, and whether there were any complications during birth. After delivery, both the mother and baby will be followed for up to 12 months. During this time, the research team will check the health of both the mother and baby and see how heat exposure during pregnancy may affect the baby's growth over time. At delivery, placental weight and volume will be collected for a smaller group of women. Breastmilk sampling will also be done for this group of women to understand the effect of high temperatures on breastmilk quality.
This study does not involve any treatment or medicine. Instead, researchers will observe the participants to learn how real-life heat exposure affects them during pregnancy. The findings from this study may help public health officials and governments find better ways to protect pregnant women and babies from the harmful effects of climate change and extreme heat, especially in places with limited resources.
Single or multiple live pregnancy confirmed through ultrasound
Gestational age less than or equal to 13 weeks and 6 days at enrollment
At least 18 years of age
Permanent resident of the study district and plans to deliver within the district
None
Pregnant women residing in peri-urban and rural areas of the three districts of Sindh, i.e., Matiari, Tharparkar and Tando Muhammad Khan
Cohort
Prospective
heat stress
Other interventionHeat stress (exposure) will be quantified using validated environmental heat stress indices, including the mean Heat Index (HI). The heat index represents the apparent temperature or how hot it feels to the human body when air temperature is combined with relative humidity. Individual-level ambient temperature heat exposure will be assessed using wearable temperature and humidity loggers.
Incidence of Low birthweight (LBW)
Defined as birth weight less than 2,500 grams (5.5 pounds). Newborn weight will be measured within 48 hours of birth using a calibrated Seca 354 infant weighing scale, precise to 0.1 kg. Measurements will be taken independently by two trained anthropometrists. If the difference exceeds 0.05 kg, a third measurement will be taken. Quality assurance procedures and calibration protocols aligned with INTERGROWTH-21st standards will be followed. LBW will be analyzed as a binary outcome (Yes/No) to assess its association with prenatal heat stress exposure across different gestational windows.
Incidence of Small Vulnerable Newborns (SVN) births
All live newborns who are either preterm, Small for Gestational Age (SGA), or Low Birth Weight (LBW)
Incidence of Miscarriage
Defined as fetal loss before 22 completed weeks of gestation. Gestational age will be confirmed at enrollment using ultrasound measurement of fetal Crown-Rump Length (CRL), with ±7 days accuracy, following INTERGROWTH-21st protocols. It will be assessed as a binary outcome (Yes/No).
Incidence of Pre-term birth
Defined as live birth before 37 completed weeks of gestation. Gestational age will be confirmed at enrollment by study physicians using ultrasound measurement of fetal Crown-Rump Length (CRL), with an accuracy of ±7 days, in accordance with INTERGROWTH-21st standards. Classification will follow standard definitions and will be recorded at the time of delivery. It will be assessed as a binary variable (Yes/No).
Incidence of Small for Gestational Age (SGA)
Description: Defined as neonates born with birth weight below the 10th percentile for gestational age and sex, based on INTERGROWTH-21st standards. Gestational age will be confirmed at enrollment using ultrasound measurement of fetal Crown-Rump Length (CRL), with ±7 days accuracy, following INTERGROWTH-21st protocols. Birth weight will be measured within 48 hours of birth using a Seca 354 infant weighing scale. Classification into term-SGA and preterm-SGA will be based on whether birth occurs before or after 37 completed weeks of gestation. Outcome will be assessed as a binary variable (Yes/No).
Incidence of Stillbirth
Defined as the birth of a fetus with no signs of life at or after 22 completed weeks of gestation. Data will also be analyzed using a ≥28-week threshold for international comparison. Gestational age will be confirmed by the study physicians through ultrasound using crown rump length (CRL). It will be assessed as a binary outcome (Yes/ No).
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