In the U.S. today, the average age at
menarche is a little over 12 years and varies according to ethnicity with U.S
black and Hispanic girls (12.1) attaining it slightly early than white girls (12.6).
The average age of thelarche and
pubarche, the first clinical signs of pubertal onset also shows a downward
trend among all groups. The age at thelarche is falling more rapidly than age
at menarche. Girls are getting the first period few months earlier as compared to
girls before 40 years but they are getting breast 1-2 years earlier.
Looking
back, the average age at menstruation was 15 years in 1900 and by 1990 it has
dropped to 12.5 at which it has very much stabilized since then.
About half of all U.S. girls show
signs of breast development by their 10th birthday, with 14 percent attaining
breast buds between their eighth and ninth birthdays.
When puberty
arrives earlier the window of exposure to estrogen widens and increases a
girl’s risk of getting breast cancer later in life. It is also associated with
many psychopathologies like anxiety and depression. Early pubic hair
development is associated with metabolic dysregulation, diabetes, and other
obesity-related disorders.
Pubertal onset is controlled by neuroendocrine
signaling which is susceptible to disruption by multiple factors. These factors change the regulation of the
GnRH secreting neurons bringing on early puberty in girls.
Over the years many genetic, environmental
and social factors have been investigated as a causative agent. Some other
factors recently investigated are physical inactivity, psychosocial stressors,
including single parent and dysfunctional families and in- utero environment.
A new study published online in American Journal of Epidemiology investigated the hypothesis than in utero exposure to
obesity and hyperglycemia leads to early puberty.
Dr. Ai Kubo of Kaiser Permanente Division of
Research, in Oakland, California and her colleagues conducted a longitudinal study
of 421 mother-daughter pairs of patients from Kaiser foundation from California
between 2005-2012.
Girls aged 6-8 years were followed
annually through ages 12-14 years. Onset of puberty was assessed using study
clinic-based Tanner staging.
It was seen that in girls whose
mother have self-reported prepregnancy BMI of 25 or greater and gestational
diabetes mellitus had significantly higher risks of earlier transition to pubic
hair stage 2, in comparison to girls whose mother were not obese or
overweight.
These girls also had earlier breast
development by average of 4 months but when other variables were considered
this association was not statistically significant.
Results of a separate cohort study
called EPOCH (Exploring Perinatal Outcomes among Children) study conducted in Colorado,
showed that exposure to maternal diabetes in utero accelerates
BMI growth in late childhood thus increasing long-term obesity risk. Obesity
itself is known factor for early puberty onset.
There has been a trend toward earlier
puberty in girls, Dr. Kubo said. "What's happened is that instead of doing
something about it, clinicians changed the standard for early puberty from 8
years old and above to 6 years and above. It's not normal because everybody's
getting it earlier. We should be doing something because there are some
consequences," she said.
In an email to Reuters health Dr.
Kubo said “Obstetrics and gynecology clinicians may want to monitor women who
are planning on becoming pregnant for their weight and lifestyle so that they
enter their pregnancy with healthy weight. Once pregnant, OB docs should
carefully monitor those who are at high risk, such as those who are overweight,
to manage their lifestyle so that they can prevent developing gestational
diabetes.”
She further added that "Kaiser
Permanente has begun system wide intervention for all the women who developed
gestational diabetes to carefully plan their diet and exercise so they don't
gain excess weight. This type of systematic intervention is very helpful not
only for the daughters' health (childhood obesity, early puberty and associated
adverse health consequences later in life) but also mothers' health outcomes
(birth complications, and later risks for diabetes, etc.)."
"Clinicians may also want to
watch girls who are developing early. Early pubic hair development may indicate
underlying metabolic dysregulation so the girls may develop childhood diabetes
or hyperglycemia, so close monitoring/treatment may be relevant for these
children," she said.
The researchers have cautioned that
this is just one study. There are other studies on early puberty but not specifically
related to maternal obesity and GDM. Further studies need to be conducted in other
population and ethnic groups to rule out the chance findings and generalizing
the results.
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