Small Head Circumference at Birth

bmjpo: first published as 10.1136/bmjpo-2019-000470 on 30 May 2019. Downloaded from PEER REVIEW HISTORY

BMJ Paediatrics Open publishes all reviews undertaken for accepted manuscripts. Reviewers are asked to complete a checklist review form and are provided with free text boxes to elaborate on their assessment. These free text comments are reproduced below.

ARTICLE DETAILS

TITLE (PROVISIONAL) Small head circumference at birth: an 8-year retrospective cohort study in China AUTHORS Liu, Shiliang; Pan, Yanmei; Auger, Nathalie; Sun, Wen; Dai, Lijuan; Xie, Sushan; Wen, Shi-Wu; Chen, Dunjin

VERSION 1 – REVIEW

REVIEWER Reviewer name: Peter Flom Institution and Country: Peter Flom Consulting, USA Competing interests: None REVIEW RETURNED 08-Mar-2019

GENERAL COMMENTS I mostly confine my remarks to statistical aspects of this paper. The general approach is fine, but I have some issues with some of the details of how it was done and some questions.

One general issue is whether neonatal head circum. is normally distributed. I looked at https://www.cdc.gov/growthcharts/html_charts/hcageinf.htm and it is not exactly normal. http://bmjpaedsopen.bmj.com/ Page 6 - first paragraph - it would be nice to give some notion of what asymmetrical and symetrical mean. My initial thought was left side of the head vs. right. (The authors define it later).

collinearty should be tested. on September 25, 2021 by guest. Protected copyright.

page 8 - line 33 - insert "below the mean" after 2SD.

page 8 - definition of various kinds of MC - if this is generally accepted as a way to categorize microcephaly, then OK, but it seems to me that it will lead to odd jumps - a baby with a 0.5 cm bigger or smaller head would be categorized very differently. Maybe the ratio of HC to weight could be used?

page 9 - don't categorize maternal age - enter it as years. Consider a spline of age as the effects are probably not linear or even monontonic. page 9 - is educational achievement of the mother a valid proxy for SES in China?

It's a matter of style, but I think (p. 10 and later) it should be "simple" and "multiple" logistic rather than "univariate" and "multivariate". The latter terms ought to disinguish models with one DV from those with several. bmjpo: first published as 10.1136/bmjpo-2019-000470 on 30 May 2019. Downloaded from p, 10 - how was the model built? Were all variables entered or did the authors use some method to select them?

REVIEWER Reviewer name: Krishika Graham Institution and Country: NYC Department of Health and Mental Hygiene. This review is that of the reviewer and does not necessarily represent the official position of the NYC Department of Health and Mental Hygiene. Competing interests: None REVIEW RETURNED 14-Mar-2019

GENERAL COMMENTS This is an interesting paper that explores risk factors for microcephaly in the Guangzhou region in China and further describes how microcephaly may contribute to other poor birth outcomes. It adds to a growing body of literature on this topic by describing risk factors in this specific population.

The authors do a nice job reviewing the basis for the study in the introduction, outline a clear method, and present their results clearly. However, the conclusion is very difficult to follow and it is unclear what main points the authors are making. I recommend that the authors make significant revisions to this section and I have provided specific comments below.

Major comments As stated above, the conclusion is difficult to follow and at times the authors contradict themselves within the conclusion section or with the results they present.

Page 12 lines 44-49: "Much of the associations were explained by a large number of infants born to mothers of Cantonese ethnicity (a http://bmjpaedsopen.bmj.com/ vast majority in Guangdong province), whose stature is smaller than women in other parts of China." • This is not supported by the data they present. The AOR for Cantonese ethnicity is not nearly as high as what they found for other risk factors like IUGR or TORCH infections. They also did not stratify by ethnicity to evaluate its interaction with other risk factors. Moreover, the authors state that the majority (85.2%) of mothers were of Cantonese origin [page 11 lines 6-9]. The population is too homogenous to make comparisons between different ethnic

populations. I would recommend that the authors remove this on September 25, 2021 by guest. Protected copyright. statement.

Page 13 lines 11-51 • It is unclear what these paragraphs are contributing to the conclusion. Perhaps the first paragraph is better placed in the introduction? Is the 2nd paragraph there to explain the significant difference in microcephaly prevalence found in Guangzhou vs what has been reported in the literature? It is unclear.

Page 15 lines 20-24: "Although there may be issues with generalizability, our study adds to the portrait of microcephaly in China, using a multi-year cohort of hospital live births with no documented evidence of Zika or other acute TORCH agents." • This statement is directly contradicted by the author’s results (elevated AOR for 'TORCH agent' reported in Tables 1 and 2) and statements throughout the conclusion section.

Minor comments Page 12 lines 35-37 bmjpo: first published as 10.1136/bmjpo-2019-000470 on 30 May 2019. Downloaded from • These are not novel markers that the authors have studied, but instead are contributing to a growing body of literature that the authors cite in this section [page 14 lines 15-17]. I would recommend that the authors tone down or consider rephrasing this language.

Page 10 lines 21-28 and Page 12 and 13 lines 53-56 and 3-6 • This model looking at microcephaly as a “fetal exposure” for poor birth outcomes did not account for some important confounders such as TORCH infections, maternal medical conditions, or teratogen exposure. • The authors should include this as a limitation in their conclusion.

REVIEWER Reviewer name: Xu Xiong Institution and Country: School of Public Health and Tropical Medicine, Tulane University, USA, Competing interests: No competing interests REVIEW RETURNED 15-Mar-2019

GENERAL COMMENTS This is a retrospective cohort study to examine the risk factors and impacts of small head circumference at birth using a large dataset from China. The methodology and analysis are sound. The authors reported several risk factors for microcephaly, and microcephaly is linked to later poor neonatal outcomes. My major comments are as follows: 1) The authors may present more clear objectives of the study: 1) to study the risk factors (maternal and periconceptional factors) for microcephaly (Tables 1-3); 2) to assess the effects of microcephaly on (in association with) the neonatal outcomes (Table 4-5). The current objectives are mix of all risk factors and neonatal outcomes together with microcephaly. http://bmjpaedsopen.bmj.com/

2) The definition of “relative” microcephaly includes “<3rd centile birth weight”. Is this a definition of IUGR by taking gestational week into account? Since “<3rd centile birth weight” is associated with severe neonatal outcomes, it is not surprised that this group of “relative” microcephaly is “associated with a wide range of adverse neonatal outcomes” (page 13). The authors may clarify this point with caution on the effect of microcephaly per se.

3) It is unclear what are differences between “maternal” and on September 25, 2021 by guest. Protected copyright. “periconceptional” factors.

4) The teratogens usually are the risk factors that lead to congenital anomalies (birth defects) and most affect very early stage of pregnancy during embryogenesis at (e.g. 3-4 weeks after conception). The authors defined the group of “exposure to teratogens” as prenatal and/or perinatal use of alcohol, cigarette or medicinal or other illicit or therapeutic drugs), but these factors are all behavioral risk factors and whether they are teratogens (i.e., causing birth defects) are still in question. There is little information on timing of exposed to these factors and whether it is maternal or paternal exposure. It should be cautious to use the term “teratogens”.

Other minor comments: 1) The authors provide the definition for TORCH infection in abstract and also in page 6, instead of it in page 9? 2) The authors provide 95% CI for all AOR in the result section? bmjpo: first published as 10.1136/bmjpo-2019-000470 on 30 May 2019. Downloaded from

VERSION 1 – AUTHOR RESPONSE

Reviewer 1

I mostly confine my remarks to statistical aspects of this paper. The general approach is fine, but I have some issues with some of the details of how it was done and some questions.

Comment 1.1.

One general issue is whether neonatal head circumference is normally distributed. I looked at https://www.cdc.gov/growthcharts/html_charts/hcageinf.htm and it is not exactly normal.

Response 1.1. Newborn’s head circumference is approximately normally distributed in large population. Generally, fetal growth standards are created for boys and girls separately based on an assumption of its normality. To avoid misunderstanding, we have reworded the sentence on line 4, page 7,

Comment 1.2.

Page 6 - first paragraph - it would be nice to give some notion of what asymmetrical and symetrical mean. My initial thought was left side of the head vs. right. (The authors define it later).

Response 1.2. We have revised as follows.

Microcephaly in the newborn is characterized by a disproportionately small head circumference for a given gestational age, and may be categorized as absolute (asymmetrical growth retardation—where the head circumference is reduced to a greater extent than length and weight) or relative (symmetrical growth retardation –where the head circumference, the length and weight are reduced to a similar http://bmjpaedsopen.bmj.com/ degree) (page 6, line 3-6).

Comment 1.3.

Page 6 - with respect to ethnicity, the authors need to be very careful. If something related to genetics is the key factor, then ethnic origin may be fine as a variable. But what if Cantonese ethnicity is associated with other variables that are linked to microcephaly? Looking at interactions with other variables might be useful. And collinearity should be tested. on September 25, 2021 by guest. Protected copyright. Response 1.3. The Cantonese people are subgroup of the Han Chinese people native to and/or originating from the province of Guangdong. We nonetheless examined interactions between Cantonese descent and other variables in our dataset (all the variables listed in Table 3) as we only found such an association in the logistic model of maternal characteristics and factors and risk of mild microcephaly. We did not find meaningful evidence of interactions and therefore did not pursue this line of inquiry. We thus added “In addition, we tested for multicollinearity among the independent variables” In the Methods (page 10, line 15). We thus added “Multiconllinearity test did not show meaningful evidence of collinearity between exposure variables.” (page 12, lines 1-2, along with results for Table 3 in Results section).

Comment 1.4. page 8 - line 33 - insert "below the mean" after 2SD.

Response 4. Done.

bmjpo: first published as 10.1136/bmjpo-2019-000470 on 30 May 2019. Downloaded from Comment 1.5. page 8 - definition of various kinds of MC - if this is generally accepted as a way to categorize microcephaly, then OK, but it seems to me that it will lead to odd jumps - a baby with a 0.5 cm bigger or smaller head would be categorized very differently. Maybe the ratio of HC to weight could be used?

Response 1.5. We used international standards for newborn weight, length, and head circumference to jointly define absolute, relative, and mild microcephaly. The ratio of HC to weight has been taken into account. (Figure 1). Our categorization of microcephaly is based on the World Health Organization’s newly developed international fetal growth standards (i.e., INTERGRWOTH-21st) is an application, with two important references (i.e., #1 and #2).

Comment 1.6. page 9 - don't categorize maternal age - enter it as years. Consider a spline of age as the effects are probably not linear or even monontonic.

Response 1.6.

The use of maternal age categories results in a model that does not assume linearity or monotonicity. Although using age as a continuous variable and fitting splines may model the empirical data more accurately, we believe that in this large dataset, the use of maternal age categories is equally justified (degrees of freedom are not a constraint). Also, using indicator variables for the traditional categories of maternal age results in easily interpretable association with maternal age. We have thus chosen to retain maternal age using indicator variables for the different categories.

Comment 1.7.

page 9 - is educational achievement of the mother a valid proxy for SES in China? http://bmjpaedsopen.bmj.com/

Response 1.7. In general, in China educational achievement is an acceptable proxy for SES. Unfortunately, no other variables on SES could be used in this analysis. Although, we did collect data on mothers’ profession/occupation, the information was too complex to be appropriately categorized and used as a proxy for SES. In the Limitations, we added that we “could not adjust for indicators of socioeconomic status (SES) apart from education.” (page 15, lines 13-14).

Comment 1.8.

It's a matter of style, but I think (p. 10 and later) it should be "simple" and "multiple" logistic rather than on September 25, 2021 by guest. Protected copyright. "univariate" and "multivariate". The latter terms ought to distinguish models with one DV from those with several.

Response 1.8. In the revised manuscript, we have changed 'univariate' to 'simple' and 'multivariate' to 'multiple'.

Comment 1.9. p, 10 - how was the model built? Were all variables entered or did the authors use some method to select them?

Response 1.9. In the Methods, we added “All variables were entered simultaneously in multiple logistic regression models. A modeling selection process was not applied.” (page 10, lines 13-14).

bmjpo: first published as 10.1136/bmjpo-2019-000470 on 30 May 2019. Downloaded from Reviewer 2:

This is an interesting paper that explores risk factors for microcephaly in the Guangzhou region in China and further describes how microcephaly may contribute to other poor birth outcomes. It adds to a growing body of literature on this topic by describing risk factors in this specific population.

Comment 2.1.

As stated above, the conclusion is difficult to follow and at times the authors contradict themselves within the conclusion section or with the results they present.

Page 12 lines 44-49: "Much of the associations were explained by a large number of infants born to mothers of Cantonese ethnicity (a vast majority in Guangdong province), whose stature is smaller than women in other parts of China."

This is not supported by the data they present. The AOR for Cantonese ethnicity is not nearly as high as what they found for other risk factors like IUGR or TORCH infections. They also did not stratify by ethnicity to evaluate its interaction with other risk factors. Moreover, the authors state that the majority (85.2%) of mothers were of Cantonese origin [page 11 lines 6-9]. The population is too homogenous to make comparisons between different ethnic populations. I would recommend that the authors remove this statement.

Response 2.1: We agree with the Reviewer. First, we have conducted multicollinearity test (page 4, line 15), and did not found meaningful evidence of collinearity between exposure variables (e.g, http://bmjpaedsopen.bmj.com/ Cantonese origin and other maternal factors) (page 12, line 1-2). Second, we revised the above statement as “Some of the associations could be explained by a large number of infants born to Cantonese mothers (e.g.,Table 3), whose statute is smaller than women in other parts of China29 although the underlying relationship is complex” (page 12, line 21 to page 13, line 2).

Comment 2.2 lines 11-51. It is unclear what these paragraphs are contributing to the conclusion. Perhaps the first paragraph is better placed in the introduction? Is the 2nd paragraph there to explain the significant difference in microcephaly prevalence found in Guangzhou vs what has been reported

in the literature? It is unclear. on September 25, 2021 by guest. Protected copyright.

Response 2.2. We have rephrased this section or removed a few sentences for clarity and explicit, now this section reads better (page 13, lines 10-14).

Comment 2.3.

This statement is directly contradicted by the author’s results (elevated AOR for 'TORCH agent' reported in Tables 1 and 2) and statements throughout the conclusion section.

Response 2.3. We rephrased the sentence to "Although there may be issues with generalizability, our study adds to the portrait of microcephaly in China, using a multi-year cohort of hospital live births with no documented evidence of Zika (page 15, lines 11-14)." We also clarified the “elevated AOR for ‘TORCH’ agent’ reported in Tables 1-3 by adding a note of “latent T. gondii only”. bmjpo: first published as 10.1136/bmjpo-2019-000470 on 30 May 2019. Downloaded from Comment 2.4.

Page 12 lines 35-37. These are not novel markers that the authors have studied, but instead are contributing to a growing body of literature that the authors cite in this section [page 14 lines 15-17]. I would recommend that the authors tone down or consider rephrasing this language.

Response 2.4: We have removed the term ‘novel’ from the statement (page 12, line 18).

Comment 2.5:

Page 10 lines 21-28 and Page 12 and 13 lines 53-56 and 3-6

This model looking at microcephaly as a “fetal exposure” for poor birth outcomes did not account for some important confounders such as TORCH infections, maternal medical conditions, or teratogen exposure. The authors should include this as a limitation in their conclusion.

Response 2.5: We appreciate this suggestion. We reanalyzed the data to include these covariates. In the Methods, we added that we adjusted for “TORCH agents, exposure to teratogens, pre-eclampsia, diabetes mellitus and chronic illness”. The newly adjusted ORs were amended in the revised manuscript (i.e. Table 4, Table 5, and Results section).

Reviewer: 3

This is a retrospective cohort study to examine the risk factors and impacts of small head circumference at birth using a large dataset from China. The methodology and analysis are sound. The authors reported several risk factors for microcephaly, and microcephaly is linked to later poor neonatal outcomes.

Comment 3.1 http://bmjpaedsopen.bmj.com/

The authors may present more clear objectives of the study: 1) to study the risk factors (maternal and periconceptional factors) for microcephaly (Tables 1-3); 2) to assess the effects of microcephaly on (in association with) the neonatal outcomes (Table 4-5). The current objectives are mix of all risk factors and neonatal outcomes together with microcephaly.

Response 3.1. We have revised as suggested as below:

We sought to identify risk factors (maternal factors or antenatal antecedents) for microcephaly, and to

assess the effects of microcephaly on neonatal outcomes (page 3, lines 3-4). on September 25, 2021 by guest. Protected copyright.

Comment 3.2.

The definition of “relative” microcephaly includes “<3rd centile birth weight”. Is this a definition of IUGR by taking gestational week into account? Since “<3rd centile birth weight” is associated with severe neonatal outcomes, it is not surprised that this group of “relative” microcephaly is “associated with a wide range of adverse neonatal outcomes” (page 13). The authors may clarify this point with caution on the effect of microcephaly per se.

Response 3.2. We agree that there is overlap between “relative” microcephaly and IUGR in this analysis, as the former is defined by both HC>3SD below the mean and BW<3rd centile (Figure 1), and the latter is defined using ICD-10 codes P05.1 and P05.9 (fetal growth retardation), which were determined by clinicians and recorded in medical charts. In this revision, we added “ (……given the significant effect of IUGR) (page 13, line 5).

Comment 3.3. It is unclear what are differences between “maternal” and “periconceptional” factors. bmjpo: first published as 10.1136/bmjpo-2019-000470 on 30 May 2019. Downloaded from Response 3.3. The data for this study are collated from hospital visits during pregnancy and delivery hospitalization. These two categories of factors cannot be differentiated. We have thus suggested to revise to “Maternal factors or antenatal antecedents” (page 7, line 9-10). The editor may decide whether this is okay. If it is not appropriate, please just use “maternal factors”.

Comment 3.4. The teratogens usually are the risk factors that lead to congenital anomalies (birth defects) and most affect very early stage of pregnancy during embryogenesis at (e.g. 3-4 weeks after conception). The authors defined the group of “exposure to teratogens” as prenatal and/or perinatal use of alcohol, cigarette or medicinal or other illicit or therapeutic drugs), but these factors are all behavioral risk factors and whether they are teratogens (i.e., causing birth defects) are still in question. There is little information on timing of exposed to these factors and whether it is maternal or paternal exposure. It should be cautious to use the term “teratogens”.

Response 3.4. We agree with the reviewer, and have added “(i.e., maternal use of substances or behavioral risk factors) including ……” (page 9, line 14) and also a new reference here (i.e., ref#27).

Comment 3.5. Other minor comments:

1) The authors provide the definition for TORCH infection in abstract and also in page 6, instead of it in page 9?

2) The authors provide 95% CI for all AOR in the result section?

Response 3.5. Both done as suggested. http://bmjpaedsopen.bmj.com/ on September 25, 2021 by guest. Protected copyright.