Analysis of Cohort Data (Kenya PNC)Unintended Pregnancy

Weiwei Zhou, Isolde Birdthistle, Susannah Mayhew - on behalf of the Integra Team

Cohort datasets • Cohort: Kenya PNC (n=869)

• Four rounds: Baseline, 6 months, 16 months, 24 months

• Study group: Intervention, Comparison

• Facility: 6 (Intervention) + 6 (Comparison)

• UID: Facility code + Interviewers’ code + Client No.

• Question: Does integration affect the incidence of unintended pregnancy?

• Method: Time to event (survival) analysis

Outcome: Event (unintended pregnancy)

Event occurred

Y = 1

Since the last time we saw you (x months ago), have you become pregnant?

1. Yes2. No3. Missing

At the time you became pregnant with the last pregnancy, did you:

1. Want to become pregnant then;

2. Want to wait until later;3. Not want to have any/more

children?4. Missing

+ (AND)=

Event did not occurY = 0

Since the last time we saw you (x months ago), have you become pregnant?

1. Yes2. No3. Missing

At the time you became pregnant with the last pregnancy, did you:

1. Want to become pregnant then;

2. Want to wait until later;3. Not want to have any/more

children?

= + (AND)

Outcome: Event (unintended pregnancy)

If Y = missing,Y is considered as 1

What did you do when you discovered that you were pregnant with your last pregnancy?

1. Nothing2. Attempted to stop but not

succeed, 3. Attempted to stop and succeed.

OR=How did you feel when you discovered you were pregnant with your last pregnancy?

1. Happy2. Unhappy/

disappointed3. Felt nothing4. other

Were you using a family planning method when you became pregnant with this last pregnancy?

1. Yes2. No

AND

Outcome: Event (unintended pregnancy)

Date of unintended pregnancy

How many

months pregnant are you?

=

xx months

Miscarried/aborted

Given birth

OR

OR

R(x-1) interview date

R(x) interview date

xx months

R(x-1) interview date

( b – a )/2

R(x) interview date

ba

R(x-1) interview date

R(x) interview date

9 months

Baseline Round 1 Round 2 Round 3

Time (from baseline interview date to event date)

1) Study Group (Intervention and Comparison)

2) Baseline index (categorical, <1.5, >=1.5)

3) Averaged cumulative index (per day).

Exposure

ACI = total index of visitstotal exposure time

0.0

1.0

2.0

3.0

4.0

5cu

mul

ativ

e in

dex

(per

day

)

0 200 400 600 800time

Exposure: cumulative index

Blue circle: Event (size of circle=level of integration) Red/Green dot: Higher/Lower ACI exposure group

Analysis plan• Cox proportional hazards model• Univariate analysis• Multivariable analysis, Adjusted for:

Demographic: age, education, religion, employment statutes, household incomeSESFertility preference: number of children, desired additional number of children, want/when to have

another child, also husband’s wish.Other: HIV status, any children died, numbers of

pregnancies• Test of model assumption

Univariate and multivariable analysis, PNC Kenya

Univariate Adjusted

n HR P-value HR P-value

Design study group

Comparison 306 Ref Ref

Intervention 563 0.63 (0.38, 1.06) 0.083 0.62 (0.32, 1.20) 0.153

Baseline index

<1.5 368 Ref Ref

>=1.5 501 2.03 (0.83, 5.00) 0.121 1.45 (0.51, 4.15) 0.488

Cumulative index

Lower 432 Ref Ref

Higher 432 1.11 (0.69, 1.78) 0.667 0.84 (0.46, 1.50) 0.549

Kaplan-Meier plot, PNC Kenya

0.85

0.90

0.95

1.00

0 200 400 600 800analysis time

Control Intervention

Kaplan-Meier survival estimates, design group

Kaplan-Meier plot, PNC Kenya

0.85

0.90

0.95

1.00

0 200 400 600 800analysis time

baseline index <= 1.5 baseline index > 1.5

Kaplan-Meier survival estimates, baseline index

Kaplan-Meier plot, PNC Kenya

0.85

0.90

0.95

1.00

0 200 400 600 800analysis time

Lower cumulative index Higher cumulative index

Kaplan-Meier survival estimates, cumulative index

Limitations and Conclusions• Index of visits to non-study clinics are not

available. Mean index values of study clinics have been used.

• Event doesn't have an uniform distribution, thus the averaged cumulative index may not represent daily/monthly exposure to clinics.

• Interaction terms• Kenya PNC: No significant effect by using

study group, baseline index, or cumulative index as exposure variable.