Interpretation
During pregnancy, the increased secretion of hormones such as estrogen,
progesterone, insulin and human placental lactogen in maternal blood
promotes the absorption of lipids in intestine.1 Other
maternal factors such as BMI, GWG, maternal nutrition, pre-pregnancy
lipid levels and various pregnancy complications may also have
significant effects on lipid metabolism and serum lipid
levels.15 It follows that there was a significant
elevation of all maternal blood lipids during pregnancy, including TG,
which helps fetus to obtain maternal lipid nutrients through placenta
for the sake of fetal development. Several population-based studies have
found that serum levels of lipids, including TG, TC, LDL-C, HDL-C and
phospholipids, increase gradually starting at gestational week 12, and
show more prominent increases during the second and third
trimesters.1, 16 The present study demonstrates that
maternal TG increase with gestational weeks throughout pregnancy,
especially rise by 3-fold from the first to third trimester, which is
consistent with previous findings.1, 17 Many factors
can affect serum lipids. Farias et al.11 found that
pre-BMI was the main factor associated gestational TG level, on account
of overweight and obese women showed higher mean TG compared with their
normal weight counterparts during pregnancy. Our results made this
conclusion even more favorable. Additionally, we found women with GDM
had higher TG level throughout pregnancy, which reached the coincident
conclusion as the study of Herrera et al..18
However, postpartum TG outcomes remain controversial. Hansen et
al.19 reported that maternal serum total lipids at 3
days postpartum was higher than the second trimester, while was declined
at 6 weeks postpartum. Mbadugha et al.20 found
maternal serum lipids dropped significantly within a week after
delivery, but returns to normal levels after about a year. Our study
indicated that maternal TG level decreased at 42 days postpartum, but is
still relatively high, which suggested that although most maternal
organs and systems can return to a normal state of non-pregnancy at 42
days postpartum, it seems that blood lipids cannot back to normal that
easily. It should be noted that non-fasting blood samples were tested at
42 days postpartum. Although fasting blood lipid test was deeply rooted,
the clinical value of non-fasting blood lipid detection has been paid
more and more attention due to support of several large population
studies.21-24 Bansal et al.23 found
that non-fasting TG levels were associated with cardiovascular events,
independent of traditional cardiac risk factors, levels of other lipids,
and markers of insulin resistance; by contrast, fasting triglyceride
levels showed little independent relationship. The European
Atherosclerosis Society (EAS) and European Federation of Clinical
Chemistry and Laboratory Medicine (EFCC) reached a joint consensus
statement to recommended that non-fasting blood samples be used as a
routine method for detecting blood lipids in April,
2016.25 The effects of pre-BMI and GDM on serum TG
continued to postpartum. We found overweight or obese and suffering from
GDM can resulted in higher TG level at 42 days postpartum, compared to
normal women, which backed up previous studies.10, 18
According to existing studies, association between postpartum TG and
gestational TG is not clear. We firstly find that TG level at 42 days
postpartum was positively associated with gestational TG. It was
reported that plasma TG metabolism is altered by age in
humans.26 Previous study found a positive relationship
between maternal GWG and several pregnancy complications, most of which
were accompanied by TG disorder.27 Considering these
factors, including maternal age, pre-BMI, GWG, GDM and gestational age
might have effects on postpartum TG level, the models of linear
regression and logistic regression analysis were adjusted for them.
Pre-BMI and GDM showed positive effects for postpartum TG in relation to
TG level at each studied gestational week in the present study.
There is no consistent clinical diagnosis for non-fasting TG level, we
defined postpartum hypertriglyceridemia as serum TG level ≥
P75 of all participants at 42 days postpartum.
Hypertriglyceridemia has been regarded as an independent risk factor for
cardiovascular disease and lipid metabolic
disorders,28 which threatens the long-term health of
women. In the present study, we proved that gestational TG levels were
positively associated with higher risk of postpartum
hypertriglyceridemia, especially in early pregnancy. The result
suggested that elevated gestational TG can be a biomarker for postpartum
hypertriglyceridemia for pregnant women. Enough attention should be paid
to the supervision and control of blood lipid level early in the first
trimester.
Considering the longitudinal design of the study, the positive
associations between gestational TG trend of change and postpartum TG
level and risk of hypertriglyceridemia were found overall. The LME model
was used instead of the difference value between TG level in the third
and first trimester, for the reason that TG level during pregnancy is a
continuous process of change. The results indicated pregnant women whose
gestational TG level elevated more significant and faster have a greater
risk of postpartum hypertriglyceridemia. It suggests that it is
necessary for pregnant women to pay attention to the elevation of lipid
level and managing through diet and exercise during pregnancy, so as to
make for postpartum health.
As a biomarker of postpartum hypertriglyceridemia for pregnant women,
gestational TG level should be concreted as a threshold or a cutoff
point to meet clinical significance. As for there is no consensual
recommended reference values of gestational serum lipids, it is always
doubtful for obstetricians to determine the status of blood lipids of
pregnant women. Wang et al.29 took adverse pregnancy
outcomes as the main outcome and presented the lipid reference range and
abnormal lipid values in early and middle pregnancy, using the cut-off
of the 95th percentiles. Our study newly set up a
prediction model of gestational TG level on postpartum
hypertriglyceridemia by using ROC curves and the Hosmer-Lemeshow
goodness-of-fit test, and found four TG cutoff points of each studied
gestational week. To find the best gestational predictive value for
postpartum hypertriglyceridemia, we selected TG cut-off by the point
nearest to the top-left most corner of the ROC curve instead of the
95th percentiles as diagnostic value, so as to ensure
optimum sensitivity and specificity. Our results provide a reference
standard for pregnant women in different trimester to pay attention to
postpartum and lifelong lipid health.
For the first time, we compared the postpartum TG outcomes in pregnant
women with different pre-BMI and between GDM and normal women.
Interestingly, the positive association between gestational TG levels
and risk of postpartum hypertriglyceridemia remained in normal weight
and overweight & obese group, but not in low weight women. Furthermore,
the risk of postpartum hypertriglyceridemia for women of normal weight
was higher than overweight & obese group in the second and third
trimester. Over the years we have been talking about the hazard of
overweight and obesity,11 but the newfangled results
suggested that the risk of gestational TG to postpartum health is even
greater for normal women. A similar case was found in the comparison
between women with and without GDM. Previous study found that high TG
levels during gestation were independently associated with an increased
risk of GDM.30 Free fatty acids (FFAs) potentially
derived from elevated TGs might decrease insulin sensitivity, creating a
vicious cycle between TG levels and insulin
resistance.31, 32 Overweight or obese pregnant women
and women with GDM themselves have lipid metabolism disorders, which
weakened some risks of adverse outcomes of elevated gestational TG.
Besides, treatments and nutrition interventions taken by pregnant women
after diagnosis of GDM may be responsible for the reduced risk of
postpartum hypertriglyceridemia. The study suggested that pregnant women
with normal pre-BMI and normal pregnancies should pay more attention to
monitoring and control of serum TG level throughout gestation, by means
of diet control, nutrition guidance and fitting exercises.