Epidemiology and statistics Test (Part 1)
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1) A 26 year old patient sustains a 3b perineal tear following delivery of her 1st baby. What is the UK incidence of OASIS (obstetric anal sphincter injury) in primiparous women?
Explanation: UK Incidence OASIS: Primiparous 6.1% Multiparous 1.7% Overall 2.9%
2) What is the incidence rate of ovarian cancer per 100,000 females in the UK?
Explanation: Ovarian cancer is the 5th most common cancer among women in the Uk with an incidence of 22 cases per 100,000 in the UK. It should be noted that ovarian tumours are very common. According to the RCOG greentop guidelines (No 62) up to 10% of women in the UK will have surgery for an ovarian mass. In premenopausal women almost all ovarian tumours are benign
3) Which of the following studies is most appropriate to assess a diagnostic test?
Explanation: Medics often think that RCT's are the gold standard of all studies. In terms of evaluating a therapy or intervention RCTs are the gold standard and top the hierarchy of evidence. This is not the case when evaluating diagnostic tests or assessing prognosis.
4) Which of the following factors as shown to decrease ovarian cancer risk?High Coffee consumption
Explanation: Factors shown to decrease risk of ovarian cancer are: Oral contraceptive use Higher Parity Breast feeding Hysterectomy Tubal Ligation Statins SLE
5) Which of the following is known to increase the risk of endometrial cancer?
Explanation: Apart from PCOS all of the above have some evidence (some of it limited) that they decrease the risk of endometrial cancer. Risk Factors for Endometrial Cancer: PCOS (2.8 ties higher in PCOS patients) Obesity (BMI >30 increases risk by 2.5 times) Late menopause Early Menarche HRT Nulliparous Diabetes (60% higher incidence in diabetics v non-diabetics) Parkinsons Tamoxifen use Diethylstilbestrol use
6) What is the incidence of placenta accreta (including increta and percreta) in the UK?
Explanation: The incidence is 1.7 per 10,000 deliveries in the UK. The USA reports incidence as high as 3 per 1000
7) A small study shows the lifetime incidence of breast cancer in smokers to be 20 in 100. In non smokers the incidence is 10 in 100. Which of the following represents the absolute risk of breast cancer in smokers?
Explanation: Don't get absolute and relative risk confused. Absolute risk is the actual risk. In this case 20 in 100 or 20%. Relative risk is a ratio of risk comparing risk in the exposed and control groups, in this case relative risk would be 2
8) Regarding uterine fibroids (leiomyoma) which of the following statements is TRUE regarding their prevalence?
Explanation: Most studies into fibroid prevalence have occurred in the US. It has been shown in a number of studies that African‐American women have a 2‐3 times more likely to develop fibroids when compared to caucasian women. Black women are also more likely to develop fibroids at a younger age. In most populations fibroids are unusual below the age of 30 but this is not uncommon in black women for these to develop in the 20's.
9) Which of the following statements regarding fibroids is FALSE?
Explanation: The risk of fibroids is actually reduced by pregnancy and decreases with an increasing number of pregnancies. Fibroids are not seen before puberty. Prevalence increases from puberty until menopause
10) What is the incidence of choriocarcinoma in the UK?
Explanation: Figures quoted vary from 1 in 40,000 to 1 in 50,000 pregnancies. Cure rates are 98‐100% in the UK.
11) Negative Predictive Value is
Explanation: The answer is D
12) What is the most common site of ectopic pregnancy implantation?
Explanation: here are about 11,800 ectopic pregnancies in the UK each year, with an ectopic pregnancy occurring in about 11 in 1000 pregnancies. Mortality rates for ectopic pregnancy in the UK are 2 per 1000. The majority of ectopics are tubal with non‐tubal ectopics accounting for only 3‐5% of ectopic pregnancies. The typical distribution is shown below
13) Positive Predictive Value is
Explanation: The answer is A
14) Which of the following studies is most appropriate to assess the efficacy of a new medication to reduce pain caused by endometriosis?
Explanation: When assessing treatment or intervention a randomised control trial is the gold standard. Note if assessing prognosis or diagnostic tests Cohort and Cross Sectional Analysis (AKA cross sectional study) respectively are optimal
15) A patient arrives on labour ward she is 37 weeks pregnant. Her last pregnancy ended with delivery via uncomplicated lower segment C‐Section 4 years ago. Contractions are 5 minutes apart and on examination and the cervix is 5cm dilated. She wants to know the risk to the baby of proceeding with vaginal delivery (VBAC). What is the additional risk the baby will have respiratory problems after VBAC compared to elective repeat C‐section (ERCS)?
Explanation: The Green-top guidelines regarding Vaginal Birth After C-section (VBAC) state the following risks with VBAC: 2-3/10,000 additional risk of birth-related perinatal death 8 in 10,000 infant developing hypoxic ischaemic encephalopathy 22-74 in 10,000 Risk of uterine rupture (previous lower segment c-section) 1% additional risk of either blood transfusion or endometritis VBAC reduces the risk of: Reduces risk the baby will have respiratory problems after birth: rates are 2 to 3% with planned VBAC and 3 to 4% with ERCS
16) Which of the following is NOT a recognised cause of hyperprolactinaemia?
Explanation: Hypothyroidism is a recognised cause of raised prolactin. In fact it is the most common cause.
17) Regarding Venous Thomboembolism (VTE) in pregnancy which of the following statements is TRUE?
Explanation: Relative risk of VTE in pregnancy is increased 4 to 6 fold in pregnancy according to the 2009 Greentop guidelines. The risk is increased further in the postpartum period and some sources quote relative risk increased up to 10 fold. Absolute risk of VTE in pregnancy and the puerperium is low at 1‐2/1000 pregnancies Incidence of Pulmonary Embolism in the UK is 1.3/10,000 maternities
18) What is the incidence of molar pregnancy in the UK?
Explanation: Figures quoted vary from 1 in 600 to 1 in 2000
19) What is the prevalence of antiphospholipid syndrome in patients with recurrent miscarriage?
Explanation: Anti‐phospholipid syndrome is an autoimmune diseases where antibodies bind to phospholipid proteins on the plasma membrane.Proteins that are bound include anticoagulants Protein C, Protein S and Factor V leading to a hyper‐coagulable state. PASS‐MRCOG | Epidemiology Lupus anticoagulant (prothrombotic antibody. Most people with Lupus don't have it. Is primary association is with antiphospholipid syndrome) binds prothrombin and cleaves it into the coagulant thrombin Antiphospholipid syndrome prevalence in the obstetric population is around 3%. In patients with recurrent miscarriage it is 15%.
20) Hypemesis gravidarum occurs in what percentage of pregnancies?
Explanation: HG occurs in approximately 1.5% of pregnancies (range is 0.5‐3.0%)
21) Sensitivity is calculated by
Explanation: The answer is B In the exam its often useful to draw the table above
22) Following a single episode of reduced fetal movements what percentage of pregnancies will be uncomplicated?
Explanation: 70% of pregnancies with a single episode of RFM are uncomplicated
23) Which of the following is a parametric test used to test correlation?
Explanation: Spearman and Pearson are correlation tests. Pearson is Parametric. Spearman is non‐parametric
24) A small study looks at medical records of deceased women to see how many smoked and how many were diagnosed with breast cancer. The results are below
Explanation: First calculate the prevalence in the control and exposed groups In smokers: 15/ (15+65) = 0.1875 In Non‐smokers 11/ (77+11) = 0.125 Then divide the prevalence in the exposed by the control group 0.1875/0.125 = 1.5
25) A new test for Group B strep has been designed and the results are shown above. Which of the below represents the Negative Likelihood ratio?
Explanation: Sensitivity = 84 / 84 +6 = 0.93 Specificity = 40 / 40 +2 = 0.95 PPV = 84/84 +2 = 0.97 NPV = 40/40+6 = 0.86 LR+ = Sensitivity/ (1‐Specificty) = 18.6 LR‐ = (1‐Sensitivity) / Specificity = 0.07
26) Regarding uterine cancer in the UK. What is the average age at diagnosis?
Explanation: The average age at diagnosis reflects which age group which is responsible for the most cases of uterine cancer. The average age at diagnosis is around 60 in the UK and the most cases of uterine cancer is seen in the 60‐64 age group (see the graph). It should be noted the incidence rate (cases per 100,000) is highest in the 70‐74 age group.
27) A new test for Group B strep has been designed and the results are shown above. Which of the below represents the Specificity?
Explanation: Sensitivity = 84 / 84 +6 = 0.93 Specificity = 40 / 40 +2 = 0.95 PPR = 84/84 +2 = 0.97 NPR = 40/40+6 = 0.86 LR+ = Sensitivity/ (1‐Specificty) = 18.6 LR‐ = (1‐Sensitivity) / Specificity = 0.07
28) Which of the following tests require the population to be of normal distribution
Explanation: The question is asking which test is parametric
29) Which of the following is the least common cause of maternal mortality
Explanation: It would be a little unfair of the RCOG to ask the leading cause of mortality as this changes and the top 3 causes swap places. The most recent data state Sepsis is the most common cause whereas the most recent Green Top Guideline (published in 2009) have VTE as the most common cause (using data from 2003‐2005). Of the options listed haemorrhage is least common
30) Regarding Pulmonary Embolism in Pregnancy which of the following statements is true?
Explanation: Sepsis is now the most common cause of maternal death in the UK based on recent figures. Prior to that Thrombosis was the most common cause. Eclampsia is the other main source of mortality. Being overweight (BMI 25‐30) has been shown to be increase risk of VTE. It is a weak risk factor however and in terms of risk stratification of pregnant women for thromboprophylaxis a BMI of >30 is considered a positive risk factor for PE by both the RCOG and SIGN (see the table)
31) Specificity is calculated by
Explanation: The answer is E
32) WHO defines the perinatal mortality rate as
Explanation: The number of stillbirths and deaths in the first week of life per 1000 live births According to WHO the perinatal period commences at 22 completed weeks (154 days) of gestation and ends seven completed days after birth The UK national figure is about 8 per 1,000 and varies markedly by social class with the highest rates seen in Asian women
33) Study Z gets funding to increase the population size from 1000 to 2000 patients. What effect is this likely to have on the results?
Explanation: Increasing sample size decreases type 2 errors and increases power of the results. Sensitivity and specificity of the test should remain constant regardless of sample size. Confidence intervals are applied by a statistician and are dependent on the mean.
34) A study looks at the average systolic blood pressure of patients in antenatal clinic. Out of 200 women the average SBP was 110mmHg and the standard error of the mean was 8mmHg. What is the 95% confidence interval
Explanation: Assuming a normal distribution, we can state that 95% of the sample mean would lie within 1.96 SDs above or below the population mean. For simplicity or to calculate a quick estimate you can use 2 rather than 1.96 Calculation of 95% CI for mean = (mean ‐ 1.96xSEM) to (mean +1.96xSEM) Upper CI limit = mean + (1.96 x SEM) Lower CI limit = mean ‐ (1.96 x SEM) SEM = 8
SEM x 1.96 = 15.68 95% CI = (110‐15.68) to (110+15.68) 95% CI = 94.32 ‐ 125.68
A patient arrives on labour ward she is 37 weeks pregnant. Her last pregnancy ended with delivery via uncomplicated lower segment C‐Section 4 years ago. Contractions are 5 minutes apart and on examination the cervix is 5cm dilated. What is the risk of uterine rupture with vaginal delivery?
Explanation: According to the Green‐top guideline No 45 the risk of uterine rupture with Vaginal Birth After C‐section (VBAC) is 22‐74 per 10,000. Remember if asked this in the exam the RCOG may ask the most appropriate risk figure from a list and may use different units e.g. as risk per 1000 or as a percentage. The correct answer may be written as 2 ‐ 8 in 1000 or 0.2 ‐ 0.8%.
36) A new test for Group B strep has been designed and the results are shown above. Which of the 6below represents the Positive Likelihood ratio?
37) Which of the following studies is most appropriate to assess a prognosis of a disease?
Explanation: Medics often think that RCT's are the gold standard of all studies. In terms of evaluating a therapy or intervention RCTs are the gold standard and top the hierarchy of evidence. This is not the case when evaluating prognostic tests which are best assessed by cohort studies
38) Which of the following has been shown to increase ovarian cancer risk?
Explanation: Of the factors listed above only HRT has been shown to increase ovarian cancer risk.
Factors shown to decrease risk of ovarian cancer are: Oral contraceptive use Higher Parity Breast feeding Hysterectomy Tubal Ligation Statins SLE
39) Regarding uterine fibroids (leiomyoma) which of the following statements is TRUE regarding their prevalence?apart and on examination and the cervix is 5cm dilated. She wants to know the risk
Explanation: Uterine fibroids are the most common non‐cancerous tumours in women of childbearing age. Although studies are limited studies have shown Approximately 60% of black women had detectable fibroids by 35 years of age; this increased to approximately 80% by 49 years of age. Approximately 40% of white women had detectable fibroids by 35 years of age; this increasedto 70% by 49 years of age.
40) Which of the following reduces the risk of fibroids?
Explanation: Pregnancy reduces the risk of fibroids COCPs are not thought to have a significant effect on prevalence but evidence is conflicting Obesity, Black ethnicity and early puberty all increase the risk of fibroids
41) A new test for Group B strep has been designed and the results are shown above. Which of the below is the Sensitivity?
42) Regarding the table above which of the below formulas would you use to calculate the positive likelihood ratio?
Explanation: Two types of likelihood ratios exist ‐ positive (LR+) and negative (LR‐). Positive likelihood ratios tell us how likely a disease is if the test is positive, while the negative likelihood ratio tells us how unlikely a disease is if the test is negative. They are calculated as: LR+ = Sensitivity / (1 ‐ Specificity) LR‐ = (1‐ Sensitivity) / Specificity A ÷ (A+C) is the calculation for sensitivity D ÷ (B+D) is the calculation for specificity A ÷ (A+B) is the calculation for positive predictive value NOTE It has been noted the RCOG may ask you for the likelihood ratio and doesn't specifypositive or negative. They have simply used sensitivity/specificity to calculate this. I can't find any statistical resources that support using this calculation method
43) The World Health Organisation define the maternal mortality ratio as
Explanation: The maternal mortality ratio is the number of maternal deaths per 100,000 live births. Maternal deathis defined by the WHO as the death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the duration and site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management but not from accidental or incidental causes Live birthis defined by the WHO as the complete expulsion or extraction from its mother of a product of conception, irrespective of the duration of the pregnancy, which, after such separation, breathes or shows any other evidence of life ‐ e.g. beating of the heart, pulsation of the umbilical cord or definite movement of voluntary muscles ‐ whether or not the umbilical cord has been cut or the placenta is attached. Each product of such a birth is considered live born
44) A new test for Group B strep has been designed and the results are shown above. Which of the below is the Negative Predictive Value?
Explanation: Sensitivity = 84 / 84 +6 = 0.93 Specificity = 40 / 40 +2 = 0.95 PPR = 84/84 +2 = 0.97 NPR = 40/40+6 = 0.87 LR+ = Sensitivity/ (1‐Specificty) = 18.6 LR‐ = (1‐Sensitivity) / Specificity = 0.07
45) A study looked at 40,000 women at a maternity unit in an area with a population of 520,000. The number of identified VTE episodes was 60 with a standard deviation of 20. Using the figures what is the standard error of the mean (SEM)?
Explanation: Standard Error of the Mean = Standard Deviation / square root of sample size SEM = SD/ square root of n SEM = 20/200 (200 is the square root of 40,000) SEM = 0.1
46) The World Health Organisation (WHO) define maternal death as
Explanation: WHO and CMACE consider maternal death to have occurred during pregnancy or within 42 days of termination of pregnancy. Maternal death is the death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the duration and site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management but not from accidental or incidental causes. To facilitate the identification of maternal deaths in circumstances in which cause of death attribution is inadequate, a new category has been introduced: Pregnancy‐related death is defined as the death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the cause of death
47) A 34 year old patient sustains a 3b perineal tear following delivery of her 3rd child. What is the UK incidence of OASIS (obstetric anal sphincter injury) in multiparous women?
A patient arrives on labour ward she is 38 weeks pregnant. Her last and only pregnancy ended with delivery via uncomplicated lower segment C‐Section 3 years ago. Contractions are 6 minutes apart and on examination and the cervix is 6cm dilated. She wants to know the chances of a successful vaginal delivery if she proceeds with a vaginal delivery after c‐section(VBAC). What is the chance of successful delivery with VBAC?
Explanation: The RCOG Green-top guidelines state successful VBAC after a single c-section is 72-76%.If a patient has had a previous successful VBAC the figure is 87-90% The success rate is lower if any of the following are present: Induced labour No previous vaginal birth Obesity (BMI >30) Previous C-section for dystocia
49) What is the incidence of obstetric cholestasis in England?
Explanation: OC Affects 0.7% pregnancies in England Itching in general affects 23% of pregnancies
50) A patient arrives on labour ward she is 37 weeks pregnant. Her last pregnancy ended with delivery via uncomplicated lower segment C‐Section 4 years ago. Contractions are 5 minutes apart and on examination and the cervix is 5cm dilated. She wants to know the risk to the baby of proceeding with vaginal delivery. What is the risk of the infant developing hypoxic ischaemic encephalopathy with VBAC?
Explanation: The Green-top guidelines regarding Vaginal Birth After C-section (VBAC) state the following risks with VBAC: 2-3/10,000 additional risk of birth-related perinatal death 8 in 10,000 infant developing hypoxic ischaemic encephalopathy 22-74 in 10,000 Risk of uterine rupture (previous lower segment c-section) 1% additional risk of either blood transfusion or endometritis VBAC reduces the risk of: Reduces risk the baby will have respiratory problems after birth: rates are 2-3% with planned VBAC and 3-4% with ERCS
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