Study design and population
From 2017 to 2020, the TSBC enrolled
women aged 18-40 years with a singleton pregnancy in the
Shuangliu Maternal and Child Health
Hospital in Chengdu, China. Details of this birth cohort have been
reported elsewhere 28.
Briefly, pregnant women who
attended antenatal care and had an gestational age ≤15 weeks were
invited to participate in our study. Women who met the following
criteria were included: 1) women aged 18-40 with a singleton pregnancy;
2) gestational age less than 15 weeks. Participants were excluded if
they 1) conceived the fetus using assisted reproductive technology, such
as in-vitro fertilization and intrauterine insemination; 2) reported
severe chronic disease or infectious disease like cancer, tuberculosis,
and HIV infection; 3) refused to sign the written informed consent or
was unable to complete the questionnaire.
Of 7281 pregnant women, 21 patients who were diagnosed with hypertension
and diabetes before pregnancy or had blood glucose ≥ 7.0 mmol/L during
early pregnancy and two pregnant women with gestational age ≥ 42 were
excluded. 374 women were missing birth outcomes, 1696 women were missing
interim sleep data, and 1282 women were missing covariate data. Finally,
5412 pregnant women were included in the analysis. A total of 5412
pregnant women were invited to complete a structured questionnaire at
≤15 weeks (first trimester) and 24-28 weeks (second trimester) of
pregnancy.
Assessment of sleep
duration
(a) During the first trimester
and the second trimester, PSQI29 was used to assess
the quality of sleep during the previous week. PSQI >5 was
defined as poor sleep quality, and PSQI≤5 was defined as good sleep
quality and was set as the control group.
(b)
Sleep duration of the past week in the first and second trimester of
pregnancy was estimated: “What time did you go to bed at night in the
past week?”, “How long does it usually take you to fall asleep each
night?”, “What time do you usually get up in the morning?”. The sleep
time was defined as the interval between the time to go to bed and the
time to get up, which was divided into four grades based on the
classification method of previous literature: ≤7 hours of nocturnal
sleep is defined as short sleep time, 8-9 hours of nocturnal sleep is
defined as adequate sleep time and control group 28, 10 hours of
nocturnal sleep is defined as the length of long sleep, ≥11 hours of
nocturnal sleep is defined as longer sleep time24,30.
(c) Nap duration of the past week in the first and second trimester of
pregnancy was estimated: ”How many minutes is the usual nap time for
nearly a week?”. Nap duration was divided into five levels:0 minutes,
1-30 minutes, 31-60 minutes, 61-90 minutes, 90
minutes31. (d) Changes in
sleep quality from the first
trimester to the second trimester were divided into four mutually
exclusive groups according to good/poor sleep quality during the first
and second trimesters: always good (Sleep quality were all good in the
first and second trimesters and were set as the control group), always
poor (Both early and middle trimesters were poor), from good to poor,
from poor to good. (e) Changes of sleep duration from the first
trimester to the second trimester were divided into four mutually
exclusive groups according to the groups of sleep duration during the
first and second trimester: always good (Both the first and second
trimesters of pregnancy were sufficient and were set as the control
group), always poor (The first and second trimesters were short or
long), from good to poor (From sufficient to short or long), from poor
to good (From short or long to sufficient). (f) Changes in nap duration
from the first trimester to the second trimester were divided into four
mutually exclusive groups according to nap duration during the first and
second trimester: always good (In the first and second trimesters of
pregnancy, the napping duration was 1-60 minutes and were set as the
control group), always poor (No napping or napping duration ≥90 minutes
in the first and second trimesters of pregnancy), from good to poor
(From 1-60 minutes to no nap or nap duration ≥90 minutes), from poor to
good (From no nap or nap duration ≥90 minutes to 1-60 minutes).
Measurement of birth
outcomes
Information on birth outcomes was
collected either through medical records. Full term was defined as 37 to
41 weeks32, and PTB was defined as less than 37 weeks
of gestation14; LBW is defined as birth weight
<2500g, macrosomia defined as birth weight ≥4000g, and normal
birth weight (NBW) defined as
weight ≥2 500 g to <4 000g 33; SGA defines
newborns whose birth weight is below the 10th percentile of the average
weight of children for the same gestational age, and larger than
gestational age (LGA) is defined as a newborn whose birth weight is
above the 90th percentile of the average weight of children for the same
gestational age 34.
Definition of variables
Pregnant women in the first trimester and the second trimester were
interviewed by trained investigators to complete structured
questionnaires on the maternal sociodemographic characteristics,
lifestyle and health status.
Age was treated as three groups: <25, 25-29, ≥30.
Employment was categorized as two
groups: unemployed and employed. Average family income was categorized
as two groups: 49,999 yuan ≤ and ≥50,000 yuan. Education was categorized
as two groups: senior high school or lower and college or above. Place
of residence was categorized as two groups: urban and rural area.
Smoking was categorized as three groups: current, former and never.
Drinking was categorized as three groups: current, former and never.
Parity was categorized as: 0 and ≥1. The Chinese version of the
Pregnancy Physical Activity Questionnaire (PPAQ) 35was used to calculate the past week physical activity energy expenditure
(MET-H/week) in the second trimester of pregnancy, which has been
validated among pregnant women in China36. The
physical activity were classified as low, medium and high. Prepregnancy
weight was self-reported by the women, and the weight of women in the
second trimester was measured by a hospital body fat meter. Weight and
standing height were measured with light clothes and no shoes.
Prepregnancy BMI (kg/m2) was calculated using
self-reported prepregnancy weight (kg) divided by height squared (m).
Prepregnancy BMI was divided into four categories: underweight
(<18.5 kg/m2), normal weight (18.5-23.9
kg/m2), overweight (24.0-27.9 kg/m2)
and obese (≥28.0 kg/m2) 37. GWG was
classified according to prepregnancy BMI and the normal values
recommended by the Institute of Medicine (IOM) 38:
Underweight 12.5 to 18.0 kg; Normal 11.5-16.0 kg; 7.0-11.5 kg
overweight; Obesity 5.0-9.0 kg. GWG within the recommended range was
defined as appropriate, below the recommended range was defined as
insufficient, and above the recommended range was defined as excessive.
Preeclampsia was divided into two groups: yes and no; HDP was divided
into two groups: yes and no; GDM was divided into two groups: yes and
no.