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Table 3 Climate factors and glucose related outcomes study table

From: Climate factors and gestational diabetes mellitus risk – a systematic review

Author, Year

Study size & location

Study Characteristics

Age range or Mean ± SD

Exposure measures

Outcome measures

Model covariates

Main Findings

Meek, 2020 [37]

n = 23,375, United Kingdom

Cohort: enrolled pregnant women with singleton pregnancies from 1/2004 to 12/2008

30.7 ± 5.6 years

Season: day of delivery

Random plasma glucose, Measured at enrollment (11–16 weeks)

Maternal age, BMI, parity, ethnicity

•Random plasma glucose levels varied significantly by season (p < 0.001) and were highest in spring (Mar-Apr) and lowest in fall (Aug-Sept)

Molina-Vega, 2020 [38]

n = 2366, Malaga, Spain

Cohort: retrospective cohort of women referred to a Pregnancy and Diabetes clinic for GDM screening

32 ± 5.2 years

A) Ambient temperature: 1) mean ∆ temp 2) mean temp Day of OGTT, 14 days pre-OGTT, and 28 days pre-OGTT

B) Season Winter (Dec 21st – Mar 20th) Spring (Mar 21st – Jun 20th) Summer (Jun 21st – Sep 20th) Autumn (Sep 21st – Dec 20th)

Glucose levels (OGTT) A) continuousB) abnormal (NDDG cut offs) Two-step: 1) 50 g GLT

2) 100 g OGTT

Maternal age

•Odds of abnormal 1-, 2-, and 3-h OGTT glucose levels were significantly higher in summer compared to autumn (e.g. 2 h OGTT glucose: OR 1.8, 95% CI: 1.4–2.4)

•Mean temperature on the day of the OGTT was negatively correlated with fasting glucose (r = − 0.08) but positively correlated with 1-, 2-, and 3-h OGTT glucose levels

Petry, 2019 [39]

n = 1074 Cambridge, United Kingdom

Cohort: Cambridge Baby Growth Study, enrolled pregnant women during early pregnancy between 4/2001–3/2009

33.4 years

Season: Winter (Dec-Feb) Spring (Mar-May) Summer (Jun-Aug) Autumn (Sep-Nov)

1) Glucose levels (OGTT)


75 g OGTT at median 28.4 weeks


•Season of OGTT was not associated with OGTT glucose levels

•Season of OGTT was not associated with HOMA S or HOMA B

Shen, 2019 [40]

n = 2120, Brisbane & Newcastle, Australia

Cohort: Women enrolled at Australian sites of the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) from 2001 to 2006

29.6 ± 5.4 years

A) Season: Winter (Jun-Aug) Spring (Sep-Nov) Summer (Dec-Feb) Autumn (Mar-May)

B) Ambient temperature (°C): Mean monthly temp

A) Glucose levels (OGTT)

B) HbA1C

C) HOMA-IR, 75 g OGTT at 24–36 weeks


•Mean fasting glucose, HbA1c, and HOMA-IR levels were lowest in the summer and highest in the winter months

•Mean 1 and 2-h OGTT glucose levels were highest in the summer and lowest in the winter

•Fasting glucose (r = − 0.145) and HbA1c (r = − 0.069) were negatively correlated with mean monthly temperature

•1 h and 2 h OGTT glucose levels were positively correlated with mean monthly temperatures (r = 0.079 and r = 0.093, respectively)

Wainstock, 2019 [33]

n = 59,882, Israel

Retrospective cohort: Included all pregnant women who underwent a GCT from 2005 to 2016 at Central District of Clalit Health Services in Israel.

29.5 ± 51 years

Seasons: Winter (Nov-Mar) Spring (April–May Summer (June-Aug) Autumn (Sept-Oct) Combined: Hot season (summer & spring) Cold season (fall & winter)

1) Glucose levels (GCT & OGTT)

2) Abnormal GCT

3) Abnormal OGTT Thresholds: Carpenter and Coustan 50-g GCT & 100-g OGTT

Maternal age and BMI

•Mean GCT glucose levels and incidence of abnormal GCT varied by season – lowest in winter, followed by spring, fall, and summer

•GCTs performed in the winter had the lowest risk of being abnormal (e.g. OR 1.58, 95%CI 1.51. 1.66, for GCT in summer compared to winter)

•No significant difference in rate of abnormal OGTT between seasons

•Results were similar when comparing warm and cold seasons

Retnakaran, 2018 [41]

n = 1464, Toronto, Canada

Cohort: enrolled pregnant women at time of GDM screening

34 ± 4 years

Ambient temperature (°C): 1) mean temp

2) daily temp change. Mean temperature: day of OGTT, 7, 14, 21, 28, 35, 42, 49, 56 days pre-OGTT. Temperature ∆: daily difference between min and max temp on OGTT day and average ∆ 7, 14, 21, 28, 35, 42, 49, 56 days pre-OGTT

1) Glucose levels (OGTT)

2) Insulin resistance (Matsuda index & HOMA-IR)

3) Beta cell function (ISSI-2 & (IGI)/HOMA-IR) 100-g OGTT in late 2nd trimester

Maternal age, ethnicity, FH of diabetes, pp-BMI, GWG through OGTT, week gestation at time of OGTT

•In covariate-adjusted models, temperature ∆ in the pre-OGTT periods (14, 21, 28, 35, 42, 49, 56 days) were positively associated with blood glucose (OGTT fasting glucose & AUCglucose)

•Temperature ∆ in the pre-OGTT periods (7, 14, 21, 28, 35, 42, 49, 56 days) were inversely associated with ISSI-2 and IGI/HOMA-IR

•Mean temperature in the weeks preceding OGTT were suggestively associated with higher OGTT fasting glucose and AUGglucose

•Stratified by season:

 temperature ∆ associated with increased OGTT fasting glucose (e.g. 28 days pre OGTT: β 0.07, p = 0.001), AUCglucose, and decreased beta cell function, in season where daily temperature is increasing (February – July)

 Mean temperature associated with increased OGTT fasting glucose (e.g. 28 days pre OGTT: β 0.039, p = 0.04), AUCglucose and suggestively decreased beta cell function, only in February–July

Vasileiou, 2018 [27]

A) n = 7618

B) n = 768, Athens, Greece

Two cohorts: A) Retrospective cohort: 7618 pregnant women who underwent a 100 g OGTT from 2002 to 2012.

B) Prospective cohort: 768 pregnant women enrolled in 3rd trimester followed over 18-month period from 1/2013 to 6/2014.

Not provided

A) Season

B) Ambient Temperature: 1) Mean monthly temperature

2) Daily temperature (9 am) Three temp groups:

1) < 24.9 °C

2) 25–29.9 °C

3) > 30 °C

Glucose levels (OGTT) Study A: 100 g OGTT in third trimester Study B: 75 g OGTT in third trimester

Maternal age, gestational age, BMI, GWG, blood pressure

Study A:

•Blood glucose levels at 1, 2, 3 h differed significantly by season – highest in summer and lowest in winter

Study B:

•Temperature was positively associated with 1 h glucose levels

•Daily temperature > 25 °C was associated with increased risk of abnormal 1 h glucose levels (RR 2.2, 95% CI 1.5, 3.3)

•1 h and 2 h glucose levels were significantly higher in > 30 °C daily temperature group

Chiefari, 2017 [42]

n = 5473 Calabria, Italy

Cohort: Study population formed based on women who underwent an OGTT for GDM screening at a hospital in Calabria, Italy from 8/2011 to 12/2016.

33 (29–36) years

Seasons: Fall, Winter, Spring Summer, Warm half & cold half of the year, 24-h average temperature each month

Glucose levels (OGTT) 75 g OGTT at 16–18 or 24–28 weeks

Maternal age, ppBMI, prior GDM, FH of diabetes

•Mean 1 h and 2 h glucose levels were highest in summer (1 h, 144; 2 h, 115) compared to other seasons

•Fasting glucose levels did not vary by season

•Higher 24-h average monthly temperature was associated with increased 1 h and 2 h glucose levels, but not fasting levels

Katsarou, 2016 [25]

n = 11,538, Skane county, Sweden

Cohort: Mamma Study, recruited women from 4 obstetric delivery departments in Skane county, Sweden from 2003 to 2005.

29.9 ± 5.1 years

Seasons: Winter (Dec-Feb) Spring (Mar-May) Summer (June-Aug) Fall (Sept-Nov) Mean monthly ambient temperature

Glucose levels (OGTT) 75 g OGTT at 28 weeks (capillary plasma glucose)

Maternal age

•Mean monthly temperature was positively associated with 2 h glucose levels, e.g. 0.009 mmol/L increase in glucose per degree (p < 0.001)

•OGTT during summer was associated with increased 2 h glucose levels

Moses, 2016 [45]

n = 7343, Wollongong, Australia

Cohort: pregnant women with OGTT medical record data from 2012 to 2014, from public and private pathology labs in the Wollongong, Australia area.

Not provided

Seasons: Summer (Dec-Feb) Fall, Winter, Spring

Glucose levels (OGTT) 75 g OGTT at 24–28 weeks, Thresholds: Modified WHO (2006)


•1 h and 2 h blood glucose were significantly lower in winter compared to the overall mean levels (p < 0.0001)

•Glucose mmol/L), median (IQR) Winter: 1 h 6.7 (5.0–7.8); 2 h 5.6 (4.8–6.6) Overall: 1 h 6.9 (5.9–8.1); 2 h 5.8 (5.0–6.7)

Janghorbani, 2006 [46]

n = 4852, Plymouth, United Kingdom

Cohort: study population based on pregnant women in Plymouth, UK screened for GDM from 1/1996 to12/1997 using data from Plymouth Child Health Database and laboratory and midwifery notes.

GDM: 30.9 ± 5.5 years, Non-GDM: 28.1 ± 5.4 years

Month and season

Glucose levels (OGTT & random plasma glucose) Random plasma glucose followed by 75 g OGTT at 26–28 weeks

Maternal age, birthweight, gestational age

•In covariate-adjusted models, month and season were not associated with glucose levels

•OGTT glucose levels did not vary significantly by month or season

Moses, 1995 [26]

n = 2749, Wollongong, Australia

Cohort: study population based on women with available OGTT data collected from clinics and obstetric offices from 1/1993 to 6/1994.

27 ± 5.1 years

Month & Season: Summer, Fall, Winter, Spring. Mean monthly ambient temperature (9 am)

Glucose levels (OGTT) 75 g OGTT at mean 28 weeks

Maternal age, parity, BMI, week of testing

•Mean monthly temperature was positively associated with 2 h glucose levels (β 0.026 mmol− 1, p = 0.01)

•2 h glucose levels differed significantly by season – highest in summer and lowest in winter (p = 0.011)

Schmidt, 1994 [47]

n = 1030, Porto Alegre, Brazil

Cohort: study subjects were women 20+ years receiving prenatal care at two university hospitals with OGTT results during 24–28 weeks gestation from 7/1991 to 3/1993.

20–45 years

Daily ambient temperature (9 am)

1) Glucose levels (OGTT)

2) Abnormal OGTT (≥7.8 mmol/L, 2 h) 75 g OGTT at 24–28 weeks

Maternal age and BMI at enrollment

•Frequency of abnormal glucose tolerance was positively associated with temperature (e.g. 10% at 20–24° vs. 4.9% at 15–19 °C)

•1 h and 2 h glucose levels were positively associated with daily temperature (0.07 mmol/L per degree increase in temperature)

  1. Abbreviations: GCT glucose challenge test, OGTT oral glucose challenge test, GDM gestational diabetes mellitus, HOMA-IR homeostatic model assessment for insulin resistance, ISSI-2 insulin sensitivity index-2, IGI insulinogenic index, AUCglucose area under the glucose response curve, WHO World Health Organization, BMI body mass index