Reviewer’s report
Title: 
Changes in physical activity across pregnancy among Chinese women: a
longitudinal cohort study
Version: 
0 
Date: 
19 Mar 2020
Reviewer: 
Kathryn Hesketh
Reviewer's report:
Thank you for the opportunity to review "Changes in physical activity across
pregnancy among Chinese women: a longitudinal cohort study". This is a
potentially interesting analysis, with a relatively large population based (I think,
from description!) sample. However, description of recruitment and also some of
the methods are lacking to allow the reader to fully determine what is going on
in this group of women. Please find my specific comments below. 
Abstract:
- Please provide time in weeks relating to early and mid-late pregnancy for
clarity
- What about consistent in/sufficient PA levels? It seems strange to specifically
focus on only increase/ decrease.
- You don't need to include p values as you have the CIs. 
- Can you say by how much PA increased by? This is an interesting and also
potentially different finding from previous studies. 
- I'm not sure your recommendations are strictly true: women who smoke may be
less likely to be active as their health behaviours differ generally, I'm not sure not
smoking will help women be more active. Also, the consistency thing may be
behavioural/ tracking as we know that people who are more active are more
likely to stay so over time. 
Introduction
- You need to include the definition 'bodily movement above rest', and qualify
occurs in a number of domains, including…
- Also include reference to PA in pregnancy being good for mental health please.
- Many countries now recommend that pregnant women are active at the same
level as non-pregnant women; given your study is conducted in China, it might
be sensible to reference a range of countries, not just the US. 
- Ln 64: tends to decrease
- Ln 69: reference change studies
- Your use of semi colon is not correct. It is better to use a ". However," in most
instances.
- Ln 73 - despite this more suitable?
Methods
- Can you explain a little more about why it is important to have the spread
across East, Central, and West China? How do the centres differ? Were they a
convenience sample? Was there a spread of SES or were they high/low income
centres? What is the health care system in China? Were they all of the same
type? 
- Was gestational age judge by LMP? 
- How many women were excluded because they couldn't remember their PA
levels? This is a potentially large source of bias as those who do less may be less
inclined to remember and could explain why your levels seem relatively high
given the cultural pressures etc. 
- Ln 107: it was updated, it was repeated - you are getting two measures. 
- Can you explain why mid-late period was chosen? Is it because you only did 2
study visits? If the range is high (i.e. 26 - 39 weeks) there may be a large range
in the PA level differences. 
- Why did you decide to dichotomize instead of using a continuous variable for
your outcome? What was the distribution of the METs in these women? 
- Do you mean univariable and multivariable? Multivariate relates to multiple
outcome variables being in the model.
- The analyses conducted don't match your proposed aims: which are a) to
investigate PA changes during pregnancy and b) determinants of PA changes
among Chinese women. You either need to revise the description of analyses or
revise your aims. 
- You state that the IPAQ was used in early pregnancy - I presume this was also
used in mid-late?
Results:
- Ln 161: Range: 26-31? Or SD?
- Please use only 1 d.p. in text; you don't really need the written description of
the characteristics as they are all apparent from the table. 
- Table 2 is in the text , but the others are positioned below. Please be consistent.
- You say characteristics by region were similar - was this all characteristics and
were all tested? Given the PA levels were different and that you mention west
china has lower SES in the discussion, I would be inclined to display
characteristic by region. 
- What counts as college? The term means different things in different regions of
the world. ]
- What do you mean by median 100% for walking? They all did walking 100%
of the time? 
- Why do you present mid-late PA only for Table 3? 
- Your determinants analysis is also missing the consistent people in Table 4?
These are an important group as well!!! Also, I really don't understand why you
have categorized into in/sufficient when you have the continuous variables for
women. You are vastly reducing the amount of information you have and
basically removing all nuance in the analyses. 
- You also don't state what analyses were adjusted for? 
- Why not just run a change analysis? Looking at how the METs actually change
in women at an individual level across pregnancy? 
Discussion
- I would like to know how the breakdown of PA changed in mid pregnancy and
later pregnancy - I presume you know which week women were measured at and
therefore whether there is a noticeable difference between mid and later
pregnancy in PA levels. 
- I disagree that bias is absolute - women's relative perceptions of PA may differ
as pregnancy progresses as they get larger etc. This may therefore influence their
perceived PA levels and self-report. 
- You state that you adjust for several variables in the discussion (though
nowhere else; please amend). What are these variables derived from? Did you
have a causal model? Why pick these? It is also probable that the confounding
variables relating to each of the potential determinants will differ, so a blanket
adjustment may not be appropriate. 
- Revise conclusions as per my suggestions from the abstract.
Are the methods appropriate and well described?
If not, please specify what is
required in your comments to the authors.
No
Does the work include the necessary controls?
If not, please specify which
controls are required in your comments to the authors.
Yes
Are the conclusions drawn adequately supported by the data shown?
If not,
please explain in your comments to the authors.
Unable to assess
Are you able to assess any statistics in the manuscript or would you
recommend an additional statistical review?
If an additional statistical review
is recommended, please specify what aspects require further assessment in your
comments to the editors.
I am able to assess the statistics
Quality of written English
Please indicate the quality of language in the
manuscript:
Acceptable
Declaration of competing interests
Please complete a declaration of competing
interests, considering the following questions:
1
. 
Have you in the past five years received reimbursements, fees, funding, or
salary from an organisation that may in any way gain or lose financially
from the publication of this manuscript, either now or in the future?
2
. 
Do you hold any stocks or shares in an organisation that may in any way
gain or lose financially from the publication of this manuscript, either now
or in the future?
3
. 
Do you hold or are you currently applying for any patents relating to the
content of the manuscript?
4
. 
Have you received reimbursements, fees, funding, or salary from an
organization that holds or has applied for patents relating to the content of
the manuscript?
5
. 
Do you have any other financial competing interests?
6
. 
Do you have any non-financial competing interests in relation to this
paper?
If you can answer no to all of the above, write 'I declare that I have no competing
interests' below. If your reply is yes to any, please give details below.
I declare that I have no competing interests
I agree to the open peer review policy of the journal. I understand that my name
will be included on my report to the authors and, if the manuscript is accepted
for publication, my named report including any attachments I upload will be
posted on the website along with the authors' responses. I agree for my report to
be made available under an Open Access Creative Commons CC-BY license
(
http://creativecommons.org/licenses/by/4.0/
). I understand that any comments
which I do not wish to be included in my named report can be included as
confidential comments to the editors, which will not be published.
I agree to the open peer review policy of the journal